Prices are definitely down.
I got SoulBlazer complete for SNES $32 US plus shipping (buy it now) on ebay 2 weeks ago.
That game is usually more than that just for the cart.
One of the local game store workers says that there's a cycle going on with the retro stuff based on the aging of the generations, and that things will be even cheaper soon.
Also, it's summertime, so people are trading things into stores moreso than in the winter.
Check out the SNES have & want lists at
http://www.angelfire.com/droid/snesshrine