Do you know if the radiator is corroded or clogged? If it is, that is why they recommend changing it. If the fan is spinning slowly, you should be able to change just the clutch which is available on this fastlane site at $150.00. The water pump must still be in good shape.
It is easy to get to the thermostat. It is right on top and the best description I can give you is it is attached to the end of the top radiator hose in the black covered housing. It looks like half of a soda can. You will find three bolts to unbolt and the thermostat is in that housing. It shouldn't take you more than five minutes to change the thermostat. Make sure the car is cool before replacing the themostat.
Hope this helps.
1987 260E Charcoal Grey 157,000 Miles
1987 260E Forest Green 120,000 Miles