Is there an affordable Power Supply capable of 12 Volts and 7 Amps?
There are plenty of decent quality 'enclosed' (you will likely have to add an external enclosure for safety etc.) switching power supplies in the $50 range with 12V output and good for more than 7A, however you may wish to determine what the requirements are for starting. As well, depending on the pump, the current may vary significantly during each cycle. You might find you actually need a 350W supply to start and run an 84W (running) pump.