ebay ram and cf card

I think $49.95 is a marginally acceptable price for 512 Mb RAM and 1 Gb compact flash (both in maximum capacity for Juno-G). As for the "CD of sounds in .wav format", well, I wouldn't count much on that.
Juno-G's RAM is actually very old, not easy to find one today, except if you are lucky (like me) and have one in your "junk yard". I've seen a 512 Mb RAM that fits to Juno-G in ebay for about half that price though. Although it says that RAM is for Juno-G, make sure it fits before buying (should be a DIMM @ 100 MHz, PC100 CL=2 or @ 133 MHz, PC133 CL=3), as described in the manual. DDR or DDR2 RAMs will not fit.
Compact flash is also a thing from the past. Make sure it comes with an adaptor, otherwise you will need to buy one for about $10.