Deck repair

[Glassport from Newport]

I am currently working on repairing my deck on my 1988 Glassport 165rx. I will also be repairing 1 stringer as well. I've learned from other threads about fibreglassing in the stringer and deckboards. Does anyone know the best place to buy fiberglass mats and resin? Also, must I use a marine only resin or are all resins similar as long as they are water proof? I've been shocked at the prices I've seen so far on boat parts web sites. Thanks for any help!