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In general, the non-breaching party is entitled to damages equal to what it would have gotten had the contract been performed. In this case, your contract damages would be $42,300. Since you have already recovered $20,000, you would be entitled to request the balance from the court. You may have additional causes of action and therefore, more damages for things such as bad faith, collateral damage (yard damage) and general waste upon the property. Alabama may also have statutory penalties such as interest on damages.
If you file suit, the contractor will likely counter-sue for damages by claiming that you somehow breached the contract and that you failed to mitigate your damages. Don't be afraid if this happens. About 75% of my practice in Mississippi & Tennessee is commercial construction litigation and I've never had a suit where the defendant didn't counter-sue the plaintiff.
It appears that you have a $50,000 +/- claim against the contractor. I suggest finding a local construction attorney to discuss this matter with you and help decide whether to file suit. Don't waste much time - there are statutes of limitations on your claim.
Let me know if you have any follow-up questions.