Mushi Futari has a greatest hits re-release, is region free, and under $40. My favorite shmup ever. The Black Label DLC is really nice too.
Deathsmiles has been released in every region and is really good too if you don't mind the lolis. It should be very affordable now.
DoDonPachi Daioujou is an awesome game, I've never played the 360 port, but I'd assume it contains all the same awesomeness (and soul crushing difficulty). Supposedly the arrange modes are pretty good in this one. Japan only.
DoDonPachi Daifukkatsu/Resurrection is good but not great. I'd recommend other games in the series over this one.
Deathsmiles IIX is available region free in the U.S. on Games on Demand and has a region locked Japanese disc release. Not too crazy over this one, the presentation isn't as good as the first game and I'm not crazy over the stage layouts. Scoring system is probably a little better than the original though.
EspGaluda II I haven't really gotten into too much, but its definitely a well made game. Standard Edition is region free, special edition is region locked.