Looking for a top-to-bottom site audit/cleanse - does this exist?

I've been running a Wordpress site for my hobby for 15+ years. I've been very lucky that things have been running smoothly, traffic has been on the rise — up until a few weeks ago when traffic (and AdSense revenue) tanked suddenly without a clear reason. I'm trying to determine the cause/how to fix it, but I simply don't have the time or knowledge to investigate and troubleshoot when someone or some service can do it more quickly. Thankfully I have a budget to work with, but first I need to know who/what I'm looking for. Any recommendations are greatly appreciated.