There is no minimum bet on freebitco.in. I have already placed multiple bets of only 100 satoshis (most of the times 1000 satoshis) without any problems.
@iv4n, 600 WOF spins, that is already a nice amount! Let us know when you spin them all and what your results are.
With 600 you may expect to grab 1 or 2 GTs, it would be great. And for sure many lottery tickets ;-)
If there is no better idea what to do, there are still 2 days to bet on crypto prize and betting on FUN would give easily 10% profit (or even more).