108-1 wing tank fuel senders
To be honest, I don't know the cost because that work was done for the guy who restored my "new" plane. Every instrument in the panel was re-done by them and they all look and act like brand new instruments. I could dig through the papers that came with the plane but the numbers would be several years out of date anyhow. It's in the hundreds of dollars, not thousands.
I would recommend calling Keystone and telling them what you have and what you want done. They could provide you with a fairly close estimate over the phone. Obviously they cannot give you an exact number until they see the instruments and/or senders but their estimates have always been very close, in my experience. I had several instruments in my "old" plane re-done over the years (turn and bank, oil temp, oil pressure, tach) and they all work great and look great. By the way, it is an extra charge to repaint the instrument faces. You can have them rework the stuff mechanically and leave the original paint if it is readable or you can pay a bit extra and the instrument faces will be freshly painted and look brand new. Either way the instrument will work like new or better than new. The repainting is purely a cosmetic decision.
Here is Keystone's contact page. You can send an electronic message or their phone number is up at the top and you can call them.
Bob and Pat and the two Stinsons