Yesterday, temporary staffing agency Kforce (NASDAQ:KFRC) (not to be confused with the fried chicken people) pre-announced that it expects its fiscal first-quarter earnings to beat Street estimates of $0.02 per share. The company expects first-quarter revenues within previous guidance; sales should come in somewhere between $129 million and $133 million. Quarter over quarter, then, revenue looks to be up by about 6%.

Combining that announcement with last Friday's news that U.S. payrolls increased by three times the expected 103,000 jobs, and the January and February job growth upgrade from pathetic to merely anemic, I thought it might be worth looking into staffing agencies as a play on the rebounding U.S. economy.

Unfortunately, all it takes is a glance at the numbers on Kforce and five of its larger competitors in the temporary and permanent employee-placement biz to see that these companies already have a lot of "rebound" expectations built into their stock prices.

Kforce has an enterprise value-to-free cash flow ratio (EV/FCF) of 26. Its five-year projected growth rate of 15% just edges out the 14% projection for the temporary staffing industry as a whole, which makes its EV/FCF/growth ratio a somewhat reasonable 1.7. Cheaper than the market as a whole, but not quite a screaming bargain.

The next best is Manpower (NYSE:MAN), which has a higher EV/FCF at 28, but the same projected growth rate as Kforce -- 15%.

Hotjobs owner Yahoo! (NASDAQ:YHOO) is not a pure-play staffer, but it has the best projected growth rate of the six companies I looked at -- 30% compounded over the next five years. Nonetheless, its EV/FCF of 105 is a little intimidating.

Even more worrisome is fellow dot-com darling Monster Worldwide (NASDAQ:MNST), whose EV/FCF of 150 dwarfs Yahoo!'s, but who plays second fiddle to Yahoo! in the growth game, clocking in at only 24%. (And, yes, with tech stocks and their nosebleed valuations, it is indeed acceptable to describe a 24% growth rate as "only.")

Finally, rounding the corner neck and neck, vying for last place, are Kelly Services (NASDAQ:KELYA) and Spherion (NYSE:SFN). The former is just about breaking even, free cash flow-wise, so its EV/FCF is in the quadruple digits. The latter is actually free cash flow negative.

To sum up, it looks like investors have already priced in expectations that the much-discussed "jobless recovery" won't stay that way forever, leaving these companies' current valuations a little too rich for me.

Tom Gardner focuses on finding companies that are undervalued and overlooked by Wall Street in Motley Fool Hidden Gems . Sign up for a free 30-day trial to learn more.

Fool contributor Rich Smith has no interest in any of the companies mentioned in this article.