What do you consider upgrades to make it a restmod?
THIS right here is key. What is it in YOUR mind that makes it a resto mod?
In a literal sense, a resto mod could be as simple as a nicely restored car (resto) with aftermarket wheels and tires, headers and exhaust (mod). If it is a redone everything with aftermarket suspension, 3rd gen Hemi, new driveline, laser straight panels and completely custom dash with a leather interior, it could be 7 figures.
So for more defined answer provide a more defined goal or a more defined budget.