I should add a disclaimer:
I am not affiliated with the sellers in any way, nor do I have any more knowledge than any other person reading the description about the item. This is simply for your reference.
I see a good number of people wanting a SPARC system to play with, and even more that want to learn HP-UX. Here's a couple of items currently on eBay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2014145973
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2014233994
Like I've said before, I once got a HP workstation with HP-UX 10.20 loaded for $25. Keep your eyes peeled, and you'll come across a good deal sooner or later!