Horrible crawlspace smell

[Houssain Alderawy]

Hello. New member here although been listening to BP for over a year now. I purchased my first rental property(single family) a couple months ago.  Every time the tenants turn off the central AC unit , a really bad smell comes from the furnace Room, which is the same smell in the crawl space. After going down there i found 5 dead mice  And threw them out. However the smell still came back and I called A crawl space remediation company. They quoted me $6500 to fully encapsulate the crawl space. 1. I spent all my money buying this property and 2. I dont think an encapsulation is even the solution. If anyone had similar experience and would like to share or just might have and opinion on what to do, please feel free to comment because I'm not sure what to do at this point. Thank you guys and sorry for the long post.