That's something you could DIY for less than a shop would charge, and it wouldn't be all that much work either. Just buy a tester like one below, along with an inexpensive fluid pump, and find out what the current coolant protection is. Then, assuming it needs to be improved, pump out the overflow tank contents. Then refill the tank with concentrated coolant, run for a day or so to fully remix the system, then test the coolant again. Just continue doing that until the protection is back to where it needs to be - probably not more than 2-3 reps would be needed to get it back to 50-50.