It was virtually a flip of the coin type decision to fix our site costs some months ago. We'd already had soil tests through Porter Davis which came back as M class, we had minimal fall (which is,as Janine says, "bugger all")so when Carlisle quoted us 10K for site costs, we were REALLY tempted to run the risk and not fix.
What we didn't know was there was an overlay on our land which I've posted about before, and we also didn't know that our slab would require some additional foundations in the form of 16 piers (which I now know are holes drilled down into stable ground and then filled with concrete for the slab to rest upon). And, thanks to fixed site costs, we don't have to pay extra for the permits and additional requirements the overlay has brought with it OR the piers. WINNER!!
I'm completely fascinated by this process. Hope I can be there on slab pour day... January 20... 23 more sleeps!!!!!