Halloween projection mapping on a budget sounds like a contradiction — projectors and mapping software have a reputation for being the expensive, pro-only part of a haunt. It isn't, not anymore. The actual budget-breaker in most displays is the props themselves: a decent animatronic witch runs $40–$100, and a big one can run far more. Projection flips that cost. You buy the cheapest, flattest props you can find — the $1.25 foam gravestone, not the $60 motorized one — and spend your money on light instead, because light is reusable every single year and a piece of foam isn't trying to be interesting on its own.
This guide is the cheap-and-cheerful version of our full Halloween decorations projection mapping guide: same idea, stripped down to the parts that cost nothing.