Actually why can't you do both of it? Bounty campaigns do not need your investments, you can participate in it and also invest your 400$ in some promising altcoin or ICO wich you choose. However If you don't have ehought time for bounty participate you can only invest.
Short term trading investment and bounty campaign are both can be done easily and even in part time but the risky is when investing short term trading especially if mistakenly choose the unprofitable coins.