Can anyone ballpark how much that would be? I guess someone
would have to come in with a york rake and get the large stone/crud out
and then seed it.

Get a couple of estimates from some local outfits and pick the highest
one. That will add legitamacy to your claim and show dilegence on your
part if the contractor is backing out on his obligation to provide your
home a lawn.

York rake, scrape removal, topsoil, seed, straw... could be at least a
few thousand. Your jaw might drop at the cost of the grass seed alone.