Where to start with a rusty block?

So I took this 2780930-340-7 (what the heck does the 7 stand for)stock 2.9.72 built bare block to a local machine shop. Their clean/ shot blasting cleanup is $100 which I thought was fair. He then took a look at the rust and said it would take a lot more. Bore, hone etc. Has anyone started with this and where did it go? I want to clean it up and sell it. Thanks340 Bare block 72.JPG 340 Bare Block 2.9.72.JPG