We just had the Isinglass replaced in one panel of our dodger by the woman at Bequia Canvas (north side of Admiralty Bay) for EC$40.00 (hourly rate; EC$60.00). She did it overnight and it was a good job. The other work I saw in her shop seemed to be top quality. You probably couldn't find a nicer place to hang out while the work is being done, as well.
We've used good sail repair places in Rodney Bay, Grenada and Bequia (hourly rate; EC$50.00), but you might be better off w/ a canvas shop, as sail repair places seem to be very busy all the time.