I have recently dug my VIC-20 out of storage and have been reliving old memories playing through my games. I also decided to build a low cost MultiCart/Development Cart for the VIC-20. You can load the eprom with multiple games. There is also a prototyping area, and access to each of the 44 edge pins (by testpoints), for those who want to do their own experimenting.
I have made a batch of these for myself & some friends, but I have plenty left over. I don't know if this would be interesting/useful for anyone here, but I have some further information on this page: http://www.gamingenterprisesinc.com/vic20/