Epoxy won’t stick to some plastics.
If you need to smooth it out, when it’s wet, why not lay a sheet of plastic over it and roll that out smooth and leave it until it’s cured. Then peel it off.
Or buy a vac pump, some plastic and some butyl tape and vac bag the fucker. (Problems solved)
[this is more than $40 - sorry]
[[do tools count in the budget?]]