C.C.
L., my husband and I are general contractors (though we do commercial work, not residential). We spend a lot of time on the bidding process, and some projects come through, and others don't.
Let's say you have a budget of $25K, and the estimate is $50K. That estimate is not the end of the world - talk to the contractor and designer and see what you can do to "value engineer" the project! Maybe the designer specified some very expensive materials - it's entirely possible you can get the same look with a less expensive material. Last time we remodeled our kitchen, the architect originally specified nearly $50K in cabinetry alone. We balked at the price, she went back to the drawing board, and came back to us with IKEA cabinets. You wouldn't believe how similar they looked to the more expensive type, and we spent only $5K on the cabinets. That was a $45K savings with no discernible difference in the look of the kitchen!
My point is, talk to the contractor and designer. Tell them you need to bring the cost way down. See what they say.
ALSO - see if the contractor will allow you to pay for materials directly. Typically we will mark up materials 15% because we have to lay out the money up front, and then carry that cost over a period of a month or two (or three) until we are paid back. If our clients pay the materials suppliers up front, that is great for us and saves them a ton of money. Likewise, you can ask that the labor quoted amount is used as a "not to exceed" amount, but that you will pay for site labor on an hourly basis. We ALWAYS quote higher than we think the actual cost will be, because we try to plan for unforeseen events. No client wants to be surprised by the final bill, so we will typically quote a little high to begin with, which leaves us with a nice profit if/when nothing goes wrong on the jobsite. So negotiate a "cost plus" contract instead of a fixed price contract.
Remember, the most expensive words you can EVER say during a remodel are, "While you're at it..." - be VERY disciplined about sticking to the original scope of work. The extras add up FAST. Read the contract carefully and make sure that everything you've talked about with the contractor is listed there. If it's not in the contract, he's not obligated to do it.
Good luck with your remodel!