Hi, thanks for submitting your question today. Generally two consenting adults can contract to about anything unless the subject matter is illegal.
There are, however, several ways to defeat contract formation (1) capacity - i.e., the parties are not mentally capable of agreeing to something, (2) mistake - the parties had a material misunderstanding of one of the terms of the contract, (3) duress - the contract was signed under threat of physical harm etc, (4) undue influence - similar to duress the contracting party was manipulated in some physical way into entering the agreement, (5) unconscionability - the terms of a contract are so materially in favor of one party so as to shock the conscious and the contracting party was essentially uneducated, uninformed and led to accepting a vastly outrageous deal , (6) fraud/deceit (fraudulent misrepresentation) - one party being intentionally misled as to what a term of the agreement may be.
In your case your best defense to contract would be one of unconscionability, especially being that the contract price is 3 x the next highest price you found. If the matter were to go to court you'd have to show that you were not aware of other prices and the painter took advantage of your lack of education in the market, and you'd have to show the price was so unfair as to shock the conscious of the court, which it probably would.
The best course of action for you at his point would be to attempt to work something out with the painter and hopefully avoid court - ask for a discount or ask to be let out of the agreement because of the other prices you've found. If this doesn't work, you'll have to decide if it is worth it for you to reject the contract and risk being sued for the project price...then go to court and claim unconscionability as a defense to the charge. It's not a clear winner for you, but you'd have a chance of voiding the agreement on this basis.
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