re: So, my builder tells me that one of his subs didn't bid my basement finish

So my opinion may be a little off only because I deal with commercial construction and not residential. However, typically GCs build in a contingency factor for when subs frick up or they do too so it doesn’t take from their bottom line and so the client doesn’t have to pay more.

In your instance of doing commercial, change orders happen with larger projects. There are a multitude of reasons why. A large factor that plays into effect is that plans aren’t the gospel. Engineers and architects do their best to plan for all factors, but real life is that there are factors in the field they would never know about or cannot account for every time. You cannot expect contractors and subs to eat cost and perform extra work because there were unknown factors that didn’t show up until the field. As a client who is building, you should always account for change orders in your budget. On a commercial job, a 1,000,000 build will never be finished with only paying 1,000,000.

If you do have change orders, carefully read their original proposals and viewing the bid documents before agreeing to anything. There is a reason why in commercial construction, many clients hire their own construction professional to handle the GC. Contractors are out to make money. If you are not knowledgeable, you can get ran over quick. Telling your contractor you won’t pay any additional money too can potentially be a breach of contract or cause further delays, leading to even higher change orders due to an increased amount of mobilizations and travel fees you have created by not letting them do the work when the issue was originally addressed.

If you or the OP are wanting an outside opinion, I would be happy to help. I’m currently a furloughed PM for the parks waiting to get back to action, so I don’t have much to do outside of watching my toddler. So let me know in this post and feel free to shoot me an email. It’s my username @yahoo.com. I can’t promise I can solve your problems as my specialty has been more of millwork, carpentry, theming (plastics, fiberglass, painting, etc) with a little electrical utility mixed in, but most likely I can at least point you in a better direction.