Depends on what they're using AWS for. OP seems to be running a simple and straightforward setup that just happens to use a lot of bandwidth. It doesn't take five full-time engineers to maintain a handful of LEMP servers.

Nothing prevents you from mixing and matching there are actually AWS services you can't find cheaper equivalents to elsewhere. My experience is that those of my consulting clients that want to migrate off AWS rarely have any problems replacing it. The cost savings usually pay back any development costs and the overall migration effort in 2-3 months at most.

If there will be 2 such companies, for that 108k I can wrote services backend that will be comptabile with AWS, so after a year you can transparently switch to that system on your bare metal and sell it to have your services for free.

I still didn't make my own "clone", because I can't afford machines to start selling it.

Hmm very unlikely. Thats 5 full time people.

More like 2 or 3 if you include overheads. Depends on location, of course.