I have a 11C and a 12C. Actually, three 12Cs.
You can find the 11Cs on eBay, but they are spendy - $200 or so.
Here is an auction, at $86 with 1 day to go, and might go for less than typical because won't appeal to a collector.
http://cgi.ebay.com/HP-11C-Hewlett-Packard-Scientific-Calculator_W0QQitemZ180120466524QQihZ008QQcategory Z58039QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
The 25th Anniversary 12C is the Platinum Edition which is slightly improved from the original 12C. Faster processor, added parentheses and undo, etc. Made by an Asian subcon for HP.
For a geeky discussion about the Platinum Edition 12C,
http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv015.cgi?read=79432
I can't use algebraic calculators, make mistakes every time I try. So I tend to pick up old HP calculators so that when/if HP gets out of the RPN calculator business, I will have a stock of calculators.