Get one on Ebay. Do a search for 2012 or 2011 (not much difference).
They sell new condition for as low as $400, but you will wait for that price. If you wait just a few days you can get a 2.3 i5 for about $450 to $500
the 2.3's are 2011, the 2.5's are 2012. The 2.3's came with 2GB (some of them) so that's a concern.
Also search with the part numbers as the listing designations will vary according to personal preference (obviously).
I have bought a few of these; very easy. They are relatively inexpensive, beautiful machines, that are fun to upgrade, and they are also lookers
note: buying and selling Apple stuff on Ebay is interesting. The stuff is so sought after, that it holds value very, very, well. It also sells quickly. THey have become true commodities, making the whole thing a rewarding, and profitable market on Ebay.