There are some other threads here on the subject that will give you valuable info but I can say this. If you start with $50, you don't leave yourself much room for variation and downswings. However, if that is all you can commit than you can still build a bankroll but just realize that realistically it will take more time. Late December 2018, I started a 10k bankroll build as an experiment. I took a couple free dollars given to me by a site, turned that into $350 and now have it spread over 3 sites and am at about $450. I can honestly say it has been one of the most stressful couple months I have ever played lol. I think the most important things to do are practice good bankroll management, choose the right games that you are strong at and play A LOT. Your only option really is playing micro's with $50 whether tourneys or cash tables. Try low stakes MTT buyins with good payouts. Play solid poker. Other excellent ways to add to your roll is by playing whatever freerolls you can find whether it is from the site itself or through forums like Cardschat
and taking advantage of deposit bonuses. Would I do it again from $0? No lol I would be much less stressed if I had just deposited the $450 and started at higher stakes but can't turn back now! I think a winning player can certainly build a good bankroll form $50 so go get 'em but I just want to stress that it takes A LOT of hands at those stakes to build. I play an average of 2000-3000 hands a day. Good luck!