He really just wants to know what the budget will be. Charge him the same as if you're doing it from scratch, because you're gonna end up starting over anyway. Go back and look at what you charged other clients for sites of similar size and charge him that amount. Explain exactly what the process and challenges are so that he understands the number. If he balks, you dodged a bullet.
Outside of a dog, a book is man's best friend. Inside of a dog it's too dark to read. Groucho Marx