If check axles, seat post, seat and clamp interface, seat itself replaceable dropouts… basically everything it has to be said.
Hopefully the bearings will cure it but I’d check everything else out too.**
Our just get bearings done and only worry about it if it’s still an issue.
As for cost, the QUAD 2 bearings in my Marin (8 in total) cost £30, labour, to replace. Mind you….had to re-do them myself anyway as they weren’t fitted properly by lbs.
Google found me some manuals, I bought some eBay genetic bearing presses and a few sockets from my toolbox to sort them out. Bit scary though, at first anyway!