Amiga ownership on a beer budget seems to be getting harder every year... It has now become a "collectible" and no longer "old junk". I know it was never "junk", but you know that old computer sitting up in the closet.
I'd suggest keeping an eye on local ads (local papers, craigslists), garage sales, etc. Try to find someone clearing out an attic or something. I bought a huge lot of amiga hardware this way (A1200, A500, software, two monitors, mice, joysticks, etc.). I kept most, and sold a couple high $ items on eBay. Made back most of the money I put out on the initial lot.