Have you LOOKED anywhere besides ebay? Like perhaps some of the vendors listed on amiga.org? An Amiga 1200 is pretty easy to get for under 200 bucks. Shell out anothe $5 on ebay for a 4 gig 2.5" drive and you've got a pretty fantastic system that will have plenty of room for all kinds of games, including the excellent AGA games that will not run on a 500, even with a hard drive.
I agree that ebay prices are retarded and not very connected to the actual worth of these old machines. However, if you want the stuff, there are other people willing to pay more than you, so theyre going to set the prices. You can complain about it, but thats not going to change the facts. If you want an Amiga with a hard drive, you can either pay a stupid price for an A500 hard drive and then have a pretty wimpy Amiga, or you can get an A1200 or A2000 for a somewhat reasonable price. The 1200 will be a much better machine. Or, you can just settle for your Amiga 500 with no hard drive.
You might find what you want for the price you're willing to pay, but I wouldn't count on that. You certainly won't find it on ebay... and I doubt you'll find one online anywhere. Maybe you'd luck out on CraigsList or Freecycle, but again... I wouldn't count on it.