None of those games are all that rare or expensive, especially Sonic 3 and SOR 1 & 2.
I didn't own Sonic 3, Ghouls n Ghosts, and Streets of Rage 1 & 2 yet. If I wanted to own the real games, I would need to spend as much as the EDMD costs. That pretty much justified it for me.
By the by, these carts are sold at http://shop.retrogate.com/ by the maker himself. The EDMD is around 61GPB in total, shipping and shell included. Put 20 aside for 3 months and you have a sweet Christmas present for yourself!