Hi Luke
I have looked into the possibility of a radio remote control and I can let you know, not to waste your money?....radio frequency has a very nasty habit of bouncing of buildings,being blocked by trees etc.
If you buy a 100m range remote, straight away you can deduct at least a third from the range, so this will only give you 75m in total distance?, if you don't have line of site of the reciever, you can deduct even more from the total, week batteries in the remote can make switching a pain, to over come this sometimes holding the remote button in for a couple of seconds may help.
Don't run the reciever on the same power supply that feeds your pump! give it its own supply.
Also ambient conditions will effect the operation ie:- Rain, fog, also strong sunlight can affect the operation.
So as you can see from the above it has a lot of Negatives to it, so unless you can over come the above problems, it will become a nightmare for you.
A radar transmitter and reciever will over come most of them, but again it has to have line of site, Not much use in our game.