The adage in investment is that out of 10 investments, six of them will fail and return nothing, two or three may last long enough to break even and one might make some profit. The hope is that the one makes enough profit to cover the other nine and beyond.
If you've only got 50k to spend, you have to be prepared to lose it all.
At 50k you're better off buying a car - one of the fastest depreciating assets you can buy - because you know that even at 2 days old, it's still worth 50% of what you paid.
Assuming you're (able to be) accredited, you have three main paths:
Shotgun: Split the money into several small batches and help several startups exist for a short while, for a tiny percentage, and prepare to be diluted out of the mix.
All in: Find one team that you love, cross your fingers.
Collaborate: Put your money in with that of others to create a larger fund, which you hope will spread the risk but still return something.