You should be looking over in mod tech. Do a lot of searching and browsing. There are a LOT of people that have asked this question in the past. But you don't say what is "big". 3 inch, 5 inch, 8 inches? Big and "on a budget" are usually mutually exclusive. If you are going big to fit tires (35's for example) you need to look at the axles- minimum new gears, maybe new everything if you have the 30/35 combo and are heavy on the skinny pedal.