Do things really need replacing right now? Either way I shall provide answers to your original question.
Replace the bushings with a quality brand that fits. There are lots of companies out there that make bushings, I will let you decide which brand works best for you. Brands like modify and Prometheus are good.
A new bearingspring guide would probably go a long towards adding longevity to your mechbox.
When your budget is a little better consider replacing all compression related components with something a little more up the ladder in quality. Replace the cylinder, piston, pistol head and nozzle. However...about your nozzle... feel free to replace it if you wish, just because its not metal doesn't mean its bad. Most nozzles are made of some form of plastic.
Bare minimum I would say is a good set of bushings, a bearing spring guide and a good quality hopup rubber to go in your hop up. I would peg that in at about $40CAD.
"Its only a little bit on fire"