Am I religiously obligated to repair the damaged exterior part of the man’s car, given that I had only agreed with him to repair the interior damages, especially since the exterior damage was minor and we did not agree upon it, and knowing that I do not have sufficient money to pay him what he is asking for?

What a person destroys of people's property, whether intentionally or by mistake, obligates him to return its value or an equivalent. If the rightful owner waives his right after it has become due, it is relinquished, even if he was unaware of its obligation. So, if there was an agreement to repair internal damages without external ones, this is considered a waiver of the right to repair external defects. However, if the agreement was specific to internal defects and did not include external ones and these were not waived, then the destroyer is obligated to repair them.