Last summer I broke a driveshaft on my 69 Mustang drag car. Was doing a burnout. Turning 6200 or so in high gear when it broke. Ouch.
I had a HD drvieshaft made at a local shop that specialized in springs and driveshafts for big trucks. They reused the yokes off my old one and used .080 wall steel tubing vs .060 stock. Also high speed balanced it. I paid $160 for the whole deal. Works great, super smooth.
I would advise to call around and get some prices though. Seems there is no set rate. I got quotes from $100 to $350.