If you're going for cheap, don't worry ahead of time about quality, just buy it. That's how I got a great F35-70 for US$11 and a Promaster (Tamron) 28-70 for US$10. If you get it cheap and don't like it, wait a month and re-sell it at for a profit. That's how I do my lens-trading. Just scan eBay LOTS and camera listings, find sales where a few lenses are offered, with or without a camera. Many kit-lens replacements can be found embedded on old cameras. Buy the package, sell off everything you don't want, use the proceeds to buy more stuff. Repeat forever.
The trick is to keep your bids within your comfort zone, plus US$5. You see a Sigma 28-80. You say to yourself, "I'd go US$15 for that." It starts at five bucks. You bid six, and wait. A minute before the auction ends, bid up to US$20.20. If you get it, great. If not, there will always be another one. Or five. It's not like these are uncommon. Just be careful when bidding on several different but similar lenses at the same time -- you might win them ALL!!