There is quite a bit to be aware of...
Do you have a copy of the full contract, signed by BOTH sides? If so, you have a ratified binding legal contract. READ the full contract and see if there is any provision in there that suggests the Builder can raise the price. I am sure, if the prices were falling, you would go back and ask for a reduction in price, right.
They cannot just "make a mistake" this is a legal document. Consult a Real Estate lawyer. Contact me if you want the name of a good one.
Also, please, people, understand, go with a Realtor to represent YOU, not the builder. They pay us, not you. If you dont go with a Realtor, they dont give you the commission they would pay us, they keep it! So you benefit by having representation on your side, your Realtor can go over the contract for and with you. Also, builders have their OWN contracts, not the regular CAR or PRDS contracts we use in the residential market, so they are different, and may have that provision in there for the builders benefit!
DID YOU TAKE A REALTOR WITH YOU? I sincerely hope you did.
Take care, be well and safe, and all the Best,
No, this is not legally right, however when new construction is concerned, the general rule of thumb is to expect up to a 10% difference from the initial quoted estimate. Wouldn't it be nice if the final price came in 10% lower than the quoted price!?!? If the "new price" is more than 10% higher than the price quoted, fight it. Your second option is to talk to another builder, or at least get other WRITTEN estimates from other local builders. Good Luck!