At this point, ebay seems your only choice. Used ones seem to be in the $75-$150 range. I bought a Z77 for $140 recently to replace an apparently dead Z68, I expect I'll try to get another one for the shelf. My 2600K CPU is still too fast to discard.
Make sure you examine the description and photos. Some ignoramuses put photos so dark you can't see anything and with such low res that you can't copy them into an editor to brighten them up and see any details.