I build a sink from MDF (fiberboard). It's cheaper than 3/4" ply and just as sturdy if you support it enough with the sink frame. I agonized over which epoxy paint to use..you can spend 100USD per gallon if you want to. I settled for a product used to paint garage floors (Valspar Epoxy Floor Paint from Home Depot or other home store). I caulked the raw seams first, then used drywall putty to form a smooth curve wherever the walls met the bottom. Let that dry, then applied two coats of paint. Nothing fancy. The trick is getting a rigid frame for the sink so it won't move when you lean on it/ against it. Oh, the floor paint cost about 50USD per gallon and I'm going to get about 4 more coats from what I have left.
Be careful installing the drain. If you recess the bottom so the drain sits below level, be sure to coat the recess, the sides of the drain hole, and the underside of the bottom with epoxy paint. Any water that creeps between the drain and the drain hole will swell the wood and it means doing it again.
Hope this helps / adds something