I had the rear window pump die on my XJ, I picked up a new one at a big box parts store. It was between $10 and $20 but don't recall exactly what I paid. Any parts store should be able to get you one and most should have it in stock.
I found using a deep socket to go over the strainer net did the trick. I had to remove the low level sensor to get to the deal pump. You may want to use a universal with the deep socket if your fill or sensor hole does not line up with the pump's attachement nut.
This is also a great time to clean out the inside of the tank. I did it to mine and when done it looked like a new tank. I did go buy a bottle brush to help me get the film off the walls.
It is a pretty easy job, just be patient when removing the filler mouth or leve sensor from the top, don't want to damage the tank.
