Title says it all.

I have one. $250

Check with AutoAtlanta, they had some NOS ones awhile back.

Wow I was hoping for under $50. Not too concerned about originality but something close would be nice. I've heard early 911 rear belts will do the trick also?

Mine are orig and I looked for a while but if they don't have to be oem then almost any lap belt should work. Just make sure the person occupying the seat won't get a face full of shifter