$75/sf is probably market for 2500-3000sf home with above-average features, not including your lot. Everyone is all over the place on their idea of what it should cost because that quote is likely just for the actual house construction plus his profit. Production builders direct costs for a home (i.e the sticks & bricks) is probably $45-60 depending on size and feature level. This does not include the lot or any margin. Most local custom (aka "pick-up truck") builders try to charge cost plus 15%. Where it gets difficult is determining the stick & brick costs in an apples to apple comparison. Some builders include permits, site prep, sewer/utility connections, bank interest, insurance, sod/irrigation and some sort of nebulous admin fee, but others will make these additional inclusions or buyers obligations. It's hard to know where they put these additional costs in the equation.
Check with others who used, him, go with your gut on if you trust him, but from what you described, it sounds market.
Just know, the process sucks, at some point you will want to fire him, your wife will cry many times and you will just "want the damn thing finished"...but once you move in, you will love the new home, and hopefully want to recommend your builder to others