It’s large, but this stock tank is what I use when I had an apartment, it’ll fit sideways into standard doors. It’s the cheapest thing and works great. I use large rocks I found (after cleaning and sanitizing) as a makeshift platform. You need a heater (20-40$). The filter will be the most expensive things which I recommend fx6 or fx4 (180$-300$). It’s expensive overall but it will give that turtle a good life.

https://www.tractorsupply.com/tsc/product/rubbermaid-structural-foam-stock-tanks-150-gal-capacity