As far as I know, bounty campaigns don't bring profits like trading. So, if I were you, I would definitely choose trading. $400 is not bad for the investment. You can get portions of Bitcoin or some altcoins like ETH or XRP (
https://cex.io/eth-btc) on exchanges like CEX. You can obtain any coin available there with fiats or major cryptos.
Agreed bounty can't bring as much profit as trading, but it does not need to invest money to be able to get profit. Just take the time to do it, investing can help you make a lot of profits in the short term, but you have to spend a lot of time on it and your mentality may be affected