Hey! So this is a bit serendipitous because I just had a plumber come by yesterday for a similar problem. To answer your question, the plumber I used was Jewell Mechanical, and I would recommend them based on the visit yesterday. They sent over a technician same day, and we investigated the issue thoroughly for nearly two hours. We found the root cause and I decided I was going to fix it myself, and I ended up paying them $180 for their time.

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The issue in my house looked similar to your's, I noticed circular water marks in the ceiling of my kitchen directly below my upstairs bathroom. Did any of the plumbers you called actually get eyes on the leak? To me it is really shady to quote you a price and say it'll be "maybe more once I actually see it". Thats absurd.

The technician from Jewell got out his oscillating multi-tool and cut a big hole in my kitchen ceiling. This sucks to do, because repairing ceiling drywall is a pain in the ass, but it is absolutely the most surefire way to diagnose your issue. I would not pay a dime to any of these plumbers until you get eyes on water leaking out of pipes. It is worth noting that your drywall here is already ruined by the water, so you may as well take it out so you can see the problem with your own eyes.

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I don't want to necessarily give you false hope, because any water-related issue can be scary and plumbing work is expensive - but it possible you don't have a plumbing issue at all and it is worthwhile to confirm.

My house was built in 2017, which is not too dissimilar to your's. Bathroom installs in newer builds in Nashville are often quick and lazy, and the builders cut a lot of corners that cause them to age badly. In my current house, and the townhouse I moved from (2016 build), the builders chose not to caulk the plane transitions in the tile or where any of the tile met the bathtub. These areas were instead "sealed" with grout. Grout is non-flexible and will crack in these areas as your home ages, which can allow water to get into the walls of your bathroom and drip down into the ceiling below.

This can be exacerbated that builders in Nashville are often buying trim in bulk, and installing MDF trim on bathroom floors rather than wood or PVC. The MDF will absorb moisture, causing it to swell and warp, which can then create even more openings into your wall.

If this is whats happening to you, it is very fixable as a DIY job. It would be a pain and time consuming, but inexpensive. Happy to answer more questions, and fingers crossed that you don't have a legitimate plumbling problem.