Yea, you can use just about anything you want. However, old games like Baseball Stars (the first generation of games) are not going to work since the chips will not physically fit on the boards. These old boards used 32 pin 8 bit roms for the sound chips, where later boards all use 42 pin/16 bit rom chips.
My price is the same as NeoGeo2k2's ($75 - includes return shipping) and the insert/sticker is $15 for the set.
I posted a sac cart list a while back and nick_th_fury was nice enogh to post this on his site.
http://nickthfury.cjb.net/
Take a look and you'll see what you can use. These are just general recomendations. If you have something particular you want to use, just ask and someone will let you know if you can use it.
!Arcade! should be posting a FAQ on conversions someday if you want to attempt it yourself. I've also been guiding a few people via e-mail, so if you want to try it and hit a snag, just drop me a line.
Jeff