LOL- sometimes that size stock tank sells for 75 bucks on Craigslist.
I start off with a cardboard box, then to a wading pool surrounded by an ex-pen (in dining room) and finally the indoor 8 x 8 x 4 foot high dog run with horse mat flooring (plus shavings) out by the laundry room. The ex-pens are used inside the run to keep them from sneaking out through the chain link and to adjust space as needed.
The horse mats give then a nonslip flooring, shavings are easy to pick up, as needed disinfecting of the mats can be in place or for total disinfection, the run and mats can be taken apart. Works for puppies too.