I would take Sprinkles advice then. Take your frame and have it sand blasted so you are down to bare metal.
There are paint stores where you can have any color you choose put into a rattle can.
Paint prep is also very important. Go to the paint store and pick out a color you like and while you're there, ask their advice on prep.
That route won't be "completely cheap" and should last ok. But as already stated, PC is tougher than paint any day of the week, especially for a trail bike that is gonna get heavily abused.