What is an unreasonable cost? It depends upon how big a workplace plan is.

If a company has less than $1 million in assets, the costs are going to be much higher than for employees who work at a place that has at least $10 million in the 401(k) kitty. Little plans are often stuck with insurance company providers, which typically assess among the stiffest fees. With insurance plans, the mutual funds or variable annuities will typically be expensive and they will often be slapped with dubious wrap fees. Most 401(k) annuities will also stick investors with onerous mortality insurance fees, which are unnecessary.

Companies should be looking for alternatives as soon as the plan acquires $1 million in assets, suggests Hal R. Schweiger, a fee-only adviser at Capital Financial Advisors in San Diego, which puts together 401(k) plans. Actually, companies of any size should be seeking bids from 401(k) vendors every three years or so in an attempt to lower costs and obtain better services.

If you're feeling helpless right about now, here is something you can do: Ask your company if it has documented your plan's fees and costs. Chances are it won't know, and that's partly because of a phenomenon I wrote about called revenue sharing: Outside 401(k) administrators and commission-based financial advisers often pick mutual funds for a workplace menu that includes 12b-1 fees that originally were supposed to be used by funds for marketing. In the 401(k) universe, the funds use this cash to pay the 401(k) administrator or plan adviser for picking it. Of course, you don't have to be a cynic to ask if the funds being selected are the best of show or simply the ones with the deepest pockets.

Typically, the administrator uses at least some of this money to cover such costs as the bookkeeping responsibility. But as the assets in a 401(k) plan grow over the years, few employers ever ask if this revenue sharing has gone beyond paying the basic expenses and mushroomed into a huge cash cow for the administrator. This can happen, since expenses such as bookkeeping and maintaining a toll-free number are pretty much fixed costs, or vary by number of employees not by the dollars in the account. The revenue-sharing money, however, can continue mushrooming, thanks to stock market gains and workers' weekly contributions.

While it's standard practice, workplace retirement plans don't need to rely upon revenue sharing to pay costs. Companies can use low-cost mutual funds for their employees that don't generate revenue-sharing cash. When going that route, employers can pick up the tab for administrative costs or pass them along to their employees. The big 401(k) players can set up these types of plans, as can fee-only investment advisory firms that routinely make sure all expenses are transparent.

For employers who blow off ERISA, here's something that might get their attention: Dozens of lawsuits have been filed against employers for failing to live up to their 401(k) responsibilities. CEOs might assume that it's the outside 401(k) administrators who risk getting clobbered in court, but they are wrong. The targets of these employee lawsuits, which should continue to multiply, are the workplaces and their executive officers.

Gulp.

Next week: One more week on 401(k)s.