I`m not a professional painter, so you can stop reading this now if you want .... I think the key to using the cheap Tractor Supply paint is to use enamel hardener. You can buy it at TSC $9 for 1/2 pint. On the last truck I painted, I shot the inside of cab without using hardener and it seemed like it never fully cured. I shot the rest of the truck using a good mix of hardener and it turned out really great.
My buddy painted my car using the flat/satin black used on caterpiller heavy equipment, It has a real nice semi gloss look , and he said it was pretty cheap.