I think he's thinking of a fuel filter. On the BMW 325 the fuel pump is located under the back seat so its pretty easy to access. You just pull up the back seat and unscrew the fuel pump out of an access panel that goes down into the gas tank.

no need to drop the whole fuel tank but they are expensive like you said, and thats why I would like to rebuild the motor myself if I had a schematic or something with all the part numbers for motor components.