Approx. How much does it cost to restore an old truck like maybe a 1938-1945 Ford Truck?

I've been working on building my detailing business and one day hopefully within the next few years I'd like to get a project truck and restore it to use as the work/company truck. I'd prefer a Ford Truck from between 1938-1945. I'd like to install a more modern engine in it for gas efficiency and A/C. Approx how much would it cost to restore one? Would I be looking at $10-15k or $30-40k?

Depends what you start with. If it's in reasonable condition, it'll cost more to buy but less to repair. If it's a basket case it'll be cheaper to buy but need more work. Quality work isn't cheap as the cost is all in the labour. I reckon you'll need $25k minimum to do a nice resto.

Well to start off, finding a decent shell for the years you want could get tricky, as those were trucks made almost 100 years ago, and most would have been crushed by the 70s. That is challenge 1. Challenge number 2 is finding any body panels that would need replacing (rust prevention was non-existent back then), finding little trim parts would be hard too. In my personal opinion I would stick with a small block ford from the 80s (small package, easy carb conversion, and some came with A/C) they are still plentiful and can produce some decent power if desired.

The biggest challenge by far is the fabrication.
My opinion you'd be looking closer to $50k to make it really nice