Worth getting a quote. Retrofitting is more expensive than a new build but it's not so bad. I got 3 patch panels with 12 runs between them and easily 25-30 drops retrofitted as well as a bunch of camera drops and all up I didn't break $2000 but there are discounts in volume. It was a 2 man job and went through two boxes of Cat6 so much more than a single run - it ends up being the equivalent of $57 per drop and that's not even counting the patch panel mounting etc etc. A more realistic price per drop for low volume is probably going to be ~$150 per drop. It might end up being worth it.
I think the base issues with multiple power line adapters and running cables between them are going to be cost, because you'll need 2 sets to do the job of one plus the cabling inbetween, and then the double hit on modulation which means your 100Mbps max quickly becomes 70 or 50 which may not be end of the world, but filtering doesn't happen at the meter and there could be cross-talk between the circuits as there's no filtering at the panel.
That said, it also might just work (albeit degraded) cross-circuit:
Do Powerline Adapters Need to Be on the Same Circuit? - Home Network Geek