Sand and filter its hard to say, depends allot on what you want. Nail guns can be expensive but it will make it easier, also going to want a chop saw for cutting your lumber, or have homedepot precut it all for you.
Just ball parking it here but I would say $150-200 in lumber, nails are cheap, maybe $20 worth of nails. For a pond liner I'd recommend the 45mil EPDM Firestone ones, used one of these in a pond with 24" motoros and never had a problem. Its $126 for the 15x15 version. Your dimensions would come out to 10'x12'
I have never fed crawfish. Blackworms and bloodworms are only really for pups and to get very picky rays to start eating. Nightcrawlers and tilapia and/or shrimp should make up most of the diet. I feed about 40% tilapia 60% nightcrawlers.