like this one for 650 but he'll take 550...... http://portland.craigslist.org/clc/cto/2649589145.html grab it and either fix the issue or just swap the motors.......everything would be there for the swap and you could do this on a weekend.
It sounds like you need to take it to a mechanic, due to the fact you live in an apartment complex that wont allow you to work on your car let alone dropping a gas tank. The Fuel Pump replacement is about a 5.5/10 Difficulty rating for a repair, but for someone whom has never done it before its around a 6.5/10..imo plus they give you a warranty!
the mechanic thinks its a hg with low compression on 3rd cy.....but yes have a shop do the work if you go the route of replacing the hg. if you do the swap....just rent a storage unit and do it there.....done that a few times i have.
So the Mechanic did a compression test on the cylinders?? (2nd opinion would do wonders...) and a swap in a Storage unit classic!