The convertible reinforcement rails come separately from the heater channels, and when I bought the rails for my '63 I recall they were about $300 for just the rails, plus about $250 for the heater channels. Factor in some steel tube to fabricate a weld-in body jig/brace and you're about $600 plus supplies (MIG wire and gas, seam sealer, welding primer, cut off wheels and grinder discs, paint) and time (lots of time). That was 10 years ago so YMMV - but suffice it to say it's a pretty major job and unless you're attached to the patina of the rest of the car, if you're going to do it you might as well go all the way and do a full resto.
My 2 cents, anyways.....
Steve