Matt's Top-5 List of acquiring used HP's:
5) Ebay - generally too expensive for me, but it's how I got some of the more desirable ones (41CV Blanknut, 32S 50th Anniversary, and got lucky on boxed 42S for $40!).
4) Trades/Classified Ads - Picked up some good ones both in the US and around the world (16C, 71B, 97, 14B 50th Anniversary, 41CX), but have had to pay/trade more than I really wanted in order to get them (I'm fair, but hey, I hate to part with more money than I have to! I'm CHEAP!)
3) Pawn Shops - Can get some good deals, but some shops are now keen on the value of HPs (thxs a lot Ebay ;-). I have bought a 17B and 28S for $7 each, both 15C and 16C for $35, both a 48S and 41CV for $25, a 48SX for $5, and an 11C for $2).
2) Garage sales/co-workers - These finds are few and far between, but I bought a boxed 45 for $5, and have been given a 41CV (my first HP!) and 11C for free from co-workers.
1) Thrift stores/Goodwill stores - By far the most frequent and generally least expensive way I pick up good HPs. I have bought a 41CV and card reader for $0.50 each, a 17BII, 21, 25, 45 for $2 each, and a boxed 21 for $1.
Oh, there's one more way I have come into newer HPs: educational services: I have been to classes/HP seminars where I have received a free 49G, a 39G and 49G for $40 and $50 each, respectively (R.I.P. Math Learning Center - HP dropped the funding), and a co-worker had 50% of his 48GX, leather case, and a math card paid by our company as college reimbursement (considered required books and materials.. well maybe not the leather case).
Deals are out there, go get'em!
Matt