I would say it's money well spent. Why expose yourselves to the health hazard or the possibility of additional chewed wiring and insulation and a fire hazard? I would get another bid, but do the work now. It's dollars spent now for clean-up and prevention or the possibility of a bigger loss later. Plus there is the "gross factor".

I live in a rural area, and while there are rats in some areas, they can be controlled. Eliminate spilled grain; keep garbage covered and remove quickly; keep wood piles away from the house; keep tree branches and shrubs away from house; keep birdhouses, seed and pet food in tight containers or away from house; set traps or poison, etc.

DO it. Do it immediately. Yes, it is expensive, but you CANNOT live in a house infested with rats. The estimate you got sounds about right. Halfway measures will NOT solve your problem.

Everything hilltop said is correct.

You do need to get at least one other bid just as a sanity check, but you said "decades" of damage, so it's not going to be cheap.