I’ve worked with a ton of builders/developers and I don’t think offering “cash” is going to help you get a better deal (definitely won’t hurt though).
I’ve never heard of a deal like this done with a builder/developer. Once a transaction is closed they want to be done with it.
I HAVE seen alot of deals structured with a “designer credit”; where the $700,000 sales price would stay intact, but the “discount” would be credited to the buyer on the HUD as a design credit.