Ratchet & Clank: Up Your Arsenal Tips

Easy money (3 things)!
The best:

When you are in Tyhhranosis any time, destroy those mushroom-like things. Use that car and hit the mushrooms and you will get 500-1000 bolts!

The second:

When in Annihilation Nation(or something that way) complete the missions again.

The third:

When in that place where Qwark is and where you can watch Qwark vid-comics, complete the arcade again. You should even complete the other missions, though.