The answer to this will depend on the circumstances under which your husband signed the contract. If the salesman visited you in your home, Pennsylvania's Unfair Trade Practices and Consumer Protection Law gives buyers a three-day right to cancel the contract (three days following the signature). The contract itself should have this cancellation language in it prominently if this was an at-home sale.
If your husband was at a hot tub store or other outside location, there is no statutory cancellation right, and his right to cancel would depend on the language of the contract itself. Hopefully you have a copy of the contract. Read through it -- even any fine print that may be there -- and see whether there is any provision for cancellation before work begins.
Even if there is no cancellation provision and the contract was done at a store location, if your husband would go back to the store in person and ask to speak with the manager, some stores will allow a purchaser to cancel if the store has not incurred any costs -- but this is purely up to the store. Those that do this do it to promote good will in the community. There's no guarantee that they will be nice guys. Practically speaking, if the amount is truly out of your budget and you can emphasize to the store that this is the case, the store may appreciate your honesty and factor into its decision the possibility that if it refuses to cancel and you can't pay the total bill, it will be saving itself some trouble by allowing you to cancel.
Of course, as with all of my online answers, my advice is limited by the brevity of your question and the facts provided. Additional information would be required to provide definitive legal advice, so this answer isn't intended to, and does not, create an attorney-client relationship.
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