at that price you might as well save yourself time and effort and buy an all-glass aquarium 180 it has the same dimensions and probably wont cost mush more. I know a place by me that sells all-glass 125's for about $250 new.
Yeah plywood tanks only start being financially viable in very big sizes. 6x2x2 tanks are very popular in glass, so much so I wouldnt even bother making one, here in Aust its cheaper to buy that size made up, my LFS sells them for ~$300AU brand new