Haha. Exactly.

A good contractor would have kept the homeowner informed of what needed to be done and the cost increase to do it as they encountered it. That way the homeowner can sign off on it (or not).

More than a few homeowners though will go an alternate route. Shop around for the cheapest contractor they can find and get them to give a quote on minimum services. Then switch it on them afterwards so the contractor will be required to do more work for the same amount quoted.

Not saying OP did this, but plumbing specs for drain and service locations are figured out long before the final fixture installation phase. Mixups do.occur, but not often (especially when contractor's reputation is on the line). So OP had a mixup that lead to the plumbing sub having to make adjustments. That should have been addressed when it happened and OP would be responsible for paying the installer more (he had more work to do, it wasn't his fault).

Having said that, money talks. Pay more for another contractor who's reasonably competent and they will find a way (even if they have to invent one) of getting concrete under the tub in a way that is minimally destructive and safe, secure, and up to code.