As Purrloin said, it's all what you're wanting to put in it. Blastoise decks can be fairly cheap to build if you're opting to only be semi-competitive, taking cards like Shaymin-EX out of the mix as it's obviously over $30 USD. With that said, most of the cards in the deck are fairly inexpensive. Archie's Ace in the Hole is around $4-$5 for a full art. Keldeo EX is also $4-$5 as well so for the most part, the whole deck is fairly inexpensive to make. I'd say if you're going the Black Kyurem EX(PLS) route, that card will be costly as it's around $25 to purchase one. Other than that, I'd say the deck is easy to build and you wont spend over $60 (if you choose not to use Black Kyruem/Shaymin EX) and you can find a variety of cards to build around Blastoise.