Can't speak to long term reliability yet, but I bought a rebuilt unit from this place...
www.airpartsonline.com
Couldn't afford new as I had just done the rebuilt tranny thing. Anyway, the part was shipped quickly, they refunded the core promptly, rebuilt unit looked like new. Been working for about 2k miles now - I live in warm, humid east central florida, so it's been "on" all of those miles. Price was 314.24 (with shipping to FLA) plus a $60 core charge.
Also sourced a drier for less than $50 from a chain, Discount Auto Parts, not sure if that's a nation-wide chain though.
I get to use the auto hobby shop at the Air Force Base (I work there), so I got the staff to pull the system down, swapped the compressor out myself in about 30 minutes, then they pumped it back down before filling it up with 134, all for $25. You'll also need a few ounces of oil (I got it donated, but that should be no more than 5 or 6 bucks). The swap is straight forward using (I think) only three sizes of sockets/wrenches. Pull off the hoses, disconect wires, loosen the belt idler (belt doesn't have to come off, and pull a couple of mounting bolts - yank it out, install by reversing the above. If you want to try it yourself , I'll go check the details.
All total, I spent slightly less than $400, even without you doing any work, it should be around $500 - IF you find a place that will let you bring in the parts (usually means they provide no warranty).