Chances are good that the only damage is the housing. You could also take it apart, and have that crack welded. Either gas with bronze rod, or with and arc welder using a special rod. Forgot the name of the special rods. I once welded the front end of a Farmall Tractor back together. It wasn't mine and I broke it, so I was forced to learn how in a hurry. I have had more than one pump on my rigs freeze and break up north that I had to gas weld the crack back together. I would imagine that any cast iron part for a jet pump is going to be at least $100.00. I don't sell Goulds, so I can't help you out on the price.
By the way, $650.00 is way too much for a 3/4hp jet pump of any kind.