For a DKB 3128, yeah, you'd have to sell a kidney or something to afford it. But the Fastlane is more reasonable: I picked one up for $150 from a private seller from comp.sys.amiga.marketplace newsgroup, and that included the 64MB of ram. You just have to look and put out little wanted posts out there. Another good place is
www.amibench.net. Put a wanted on there and on the newsgroup, and hopefully somebody will contact you. And if you're seeing asking prices of $200+, then you really want to consider saving a few more dollars and getting a good accelerator with the memory slots on it. You won't be sorry with that option!
-David