This scenario used to unfold in the offices of individual planners or big accounting firms. But now Wall Street has discovered that financial soothsaying is a great marketing tool and is dangling financial plans in front of customers the way banks used to display toasters. The bait: rock-bottom prices.

But how well do these canned plans serve consumers? To find out, I subjected my family’s finances to the scrutiny of planning services from three firms. My husband and I had plenty of room for improvement. We’re both self-employed, so neither of us has a corporate-sponsored pension fund (or those account-fattening corporate contributions). We also have to buy our own disability, health and life insurance, some of which we’ve neglected to do. We’re pretty good savers but conservative investors. And we invest separately, so that our portfolio, if you can call it that, looks like our basement: stuff everywhere.

I picked Prudential’s Personal Financial Architect because it was free. I chose Merrill Lynch’s Financial Foundation because it was cheap ($175) and heavily advertised. Then I splurged on a $1,500 plan from American Express’s Financial Advisors. Though much more expensive than the others, it was still less costly than the $3,000 or more charged by many independent fee-only advisers.

The results: there were only two similarities among the plans. Each came up with a nearly identical multimillion-dollar figure for our assets at retirement. Clearly that part isn’t rocket science. And each tried to get us to dump our mutual funds in favor of new ones that would earn them commissions–without researching our holdings well enough to make a persuasive case. I found other reasons to feel smarter than the planners, but, to my smug surprise, I learned a thing or two. Here’s how my three plans stacked up and the lessons I took away:

Sorry, Prudential, but your ““planning’’ product was such a transparent bid for new prospects I expected to see miners’ lamps on the brokers’ heads. I spoke by phone to a broker who asked me 25 or so questions. A week later, a boy who looked alarmingly like my 14-year-old babysitter introduced himself as the broker who’d collected my vital statistics. He was in training, he confessed sheepishly, so someone else would be handling our plan.

Broker No. 2 materialized and explained, as he guided us toward a small conference room, that he hadn’t been trained on the computer yet, so his boss would present our plan. I was getting the feeling that Prudential hadn’t agonized over the subtleties of our financial position.

Broker No. 3 had good news. We’d be able to meet our retirement objective if we carried out the aggressive saving program I had optimistically outlined. Did we want to adjust any assumptions about inflation, our retirement age or the rate of return we expected on our investments?

This is the key feature of the Architect service. Brokers can instantly change any key variable and demonstrate the results in brightly colored bar charts on a computer right in front of you. While that’s handy, it’s not really enough. The Architect doesn’t consider expenses, tax strategies, saving for college, insurance needs or estate planning. Prudential has since enhanced the part of the program that recommends how assets should be divvied up among stocks, bonds and cash–which is good because our brokers skipped it in favor of The Pitch: ““There’s no pressure here, but we’d like to manage all of your money.''

At least they were upfront about it. You should use the Architect rather than Quicken Financial Planner only if you don’t have a computer–or if you’re paralyzed by financial issues. Even then, consider this a warm-up exercise for the real thing.

I’m sure that Merrill, like Prudential, popped data into a computer to produce my 70-page, hardbound plan. But its service was more impressive.

First a broker came to our house to help us fill out the questionnaire. That’s a big help for neophytes or procrastinators. And the extra information Merrill asked for allowed it to customize its recommendations to a surprising degree. I learned that I need $59,400 in disability insurance, $400,000 or more in life insurance and an additional $5,200 in annual savings to send our two kids to private colleges–all surprisingly close to the figures produced by my pricey American Express adviser.

The written plan was equally ambitious on other topics, particularly income tax and estate planning, but not helpful about what I should do. After describing how an irrevocable trust could shelter my estate from taxes, for example, the report described a trust’s downside (I’d never be able to change it) and told me to consult my attorney. What I really wanted was someone smart to tell me if I should do it. The broker who delivered my book didn’t oblige. He wanted to replace a handful of our bond funds with shares in Microsoft, Fannie Mae and Merrill Lynch Pacific Fund, which has a 5.25 percent sales charge. Reason? The taxable income generated by my funds ““does not match your objective.’’ If you want to use this service, ask to have the written plan delivered before you meet with the broker, so you can study it. Then press him to go through every section, even if you don’t think you need to.

The American Express plan blew away the competition, as it should have considering the price. What made this service an eye-opener was that so many strategies dovetailed with each other.

For example, I had been resisting buying life insurance for years. Left to my own devices I would have eventually bought it using price as my only consideration. But because my adviser forced me through a discussion on estate planning, which seemed bizarre at the age of 42, I realized that the smart thing to do was to have an irrevocable trust own our policies. That way the insurance proceeds are protected from estate taxes and I won’t face the complicated chore of transferring ownership of my insurance policy into a trust later on. My adviser also saved me from establishing the wrong kind of retirement plan. If she hadn’t intervened I’d have merrily overfunded my retirement for God knows how long before the IRS caught up with me.

I had a few beefs about this service, too. It took more than three months to get the plan. My adviser didn’t tell me that I could have elected to get a much cheaper plan (chart) or that she stood to earn commissions on the products she recommended.

Recognizing such potential pitfalls is critical if you’re going to use one of the new low-cost planning services. After all, they’re priced cheaply for a reason. As long as you understand that, you’ll be able to enrich yourself–and Wall Street, too.