I do not know about the filters and stuff but I am building things out of styrofoam blocks and pouring in concrete its amazingly cheap to build...keep in mind this is isolated from both sides, and you just call a truck to pour in the concrete...my indoor pool will be around 1000$ to pour and maybe another 500$ for some impregnated concrete finish...you stack the molds as lego bricks....3 of them is 1m2...
