Price is usually about $30 per regulator (1st or 2nd), plus $30 for each kit to overhaul each one. That makes $60 per reg, then multiple by 3 regulators per diving kit and it's $180. If you have 2 sets, then you're looking at $360.
That cost really isn't too bad. If you were to get your car repaired at an auto-shop they'd charge $90 an hour plus parts. Think of it like paying for 2 hours shop time for doing the 2 regulator kits, and the rest in parts cost. I think most people would consider that reasonable.
It probably wasn't absolutely necessary to overhaul them but no harm done - you're set for another 1-2+ years.
The other option is to learn how to do the overhaul yourself, which is doable and many divers do it. However, it still takes time to learn how to do it, and to actually perform the overhaul. You have to track down the correct parts or substitutes and kits which may not be readily available to DIY'ers. If a person is wanting to go this route, they often purchase regulators they know they can easily get parts for and they don't need propitiatory tools to be able to work on.
Some people argue that the Regulator is the most important dive equipment to be maintained. The truth is, your buoyancy compensation and dry suit inflation/deflation are just as important and is often the most neglected dive gear part that leads to diving accidents. Make sure those are cleaned, serviced, and working well.