Difficult to say with out seeing it but I buggered my Pryde Alpha 5.4 on saturday and got it fixed the next day for not to much. Suggest you take it to a local sail maker for a quote. FYI I used Ullman sails in Mornington.
I had a complete panel replaced a while back with full x-ply $200 on a 6.5m. This was a bit on the expensive side, altho an excellent job. That panel was stronger than any other part of the sail.
Recently had clew ripped out and replaced $80. Because these guys make clews for yachts it was way stronger than the original and is still going strong. This one was definately worth it.
All done at Quantum sails Mornington. They specialise in yacht sails but easily adapt it for windsurfers except when it comes to specialised parts like battens.
Now I wouldn't pay anything more than $150 for anything since I've been able to get a great condition used windsufer sail for $150 and less.