In March of this year, we received a bid on SIPS. We actually placed our deposit in June. When we received the invoice for the balance, we were told that there had been a 4% increase on the total bid due to petroleum in the materials. Doesa this sound accurate?

kjb;

not much you can do about it , unless you had a price guarantee. As builders we face cost increases all the time on LS contracts and have to eat it. 4% seems pretty modest

Yes. I have seen R-Control out of Denver increase prices twice, each by 7%. They also stated that the increases were based on the higher costs to manufacture EPS(no doubt petroleum based).

Sounds like you got screwed by an unscrupulous provider. Why did you pay a "deposit"
for a price that was not agreed on ahead of time?

Lesson is DO NOT PAY A DEPOSIT for an estimate and get competitive bids.

Don't let someone jive you with an "estimated" cost. An estimate is an estimate.
A bid is a bid. You don't have to fork over any cash for a bogus estimate that
is almost certain to be higher.