Hey bud, really depends on what you want to spend, and what you can still find...
1st option is to strengthen the frame you already have by bracing it, im sure someone can link a thread on doing that..
Otherwise there are plenty of options just finding a nice one can be hard, in the day the top picks would have been , Five0, Red baron, Sano, Billetware and the like but they are getting harder and harder to find in good condition as most aren't made anymore, I believe fast50's still do a good 50 frame, my personal fav is the billetware cradle mount which my 88 is built up on now but I got mine from the states, another option is the original thump pro cnc frame its pretty trick looking and can take a beating, bare in mind all of the above mentioned frames are going to be a bit heavier than stock..