Re-building sets - paid services? My son has A LOT of LEGO sets, which have sadly broken down into many, many millions of pieces. Does anyone know of any paid services that might help re-build his sets.

I know this sounds like it goes against the principles of LEGO, but really it's just too daunting, and he's lost interest because of it.
With “services”, do you mean someone who would come out to your house and rebuild the sets for you? As intriguing as that sounds, I do not believe something like that exists. Your best bet is to grab an instruction manual and start rebuilding from the pieces. Once you have a few sets built this way, it’ll become easier to rebuild the remaining sets. For sets that you know he has but you cannot find a manual, go to lego.com to download the instructions. Then, once it’s down to a few unknown sets, make pictures of the unusual pieces and post them here - we can help you identify the set(s).