This can take a while to get the desired amount of bolts you need, but it does work. Simply go to the Thug Rendevous, and do the second mission, the one where you have to kill 30 space wasps. You need the nuclear device. Simply aim the crosshairs slightly downwards at the start and fire the nuke. The nuke will destroy all 30 space wasps in 3 seconds, completing the mission and earning the reward. Do this multiple times for easy money.(Note: You only get 6000 bolts in challenge mode. You only get 600 bolts in normal mode)