+1 on the POC
If you just want a rollbar Autopower in San Diego makes and sells a bolt-in "Race" rollbar for under $550. They also make weld-in and bolt-in cage kits but the fit and design doesn't compare to a quality custom cage.
here's some info at IO Port's site, Autopower sells direct too for the same prices so you don't have to ship:
IO Port Racing Supplies: 911, 912, 930, 964 1963 - 1993