I know many on SCF are familiar with Buck-a-Cover, but for those who haven't linked to the site lately, I just found that there is a special "housecleaning sale" going on where Special Event Covers of the 30's and 40's are going for only 40 cents apiece ... and first day covers of stamps and postal stationery items from the 60's and 70's are 50 cents apiece.
Some may find it worth checking out. Many of those Special Event covers have nice handstamped cachets, and a few have cinderella stamps attached, too.
http://www.buckacover.com/index.shtml