Before dropping the money on one, look into a skunkboard. This is the Jag version of a Mega Everdrive or other emu cart EXCEPT there is no SD compatibility. You hook it up to a PC and flash the ISO/ROM onto a skunk. It is difficult to get typical ROMs of commercial games to run off it, but several devs will release their games for free (either for a DL and burn onto a CD-R or via skunk). It was made for the homebrew community, not to play retail games for free but it'll allow you to access many homebrew titles.
Most importantly, don't buy a Jag CD from ebay. Go to the Best Electronics website. Although their site is straight out of 1992, they're a good group of dudes. They sell refurbished Jag CD (packed in foam just no outer box) for cheaper than ebay & they have a 90 day warranty.
Hope this helps!
Best retail JCD release - Battlemorph (large jump from it's little brother)