divide your $50 by the number of days trial you want, say 25 days = $2 cap on your daily spend, this would be for rock bottom keys so maybe a better setting of say $5 = 10 days. ? you make the choice

next your max cpc will depend on keys, used, the position you wish to tarhet the Q score and many other variables.

good luck

You're going to pretty much spend that on testing and learning. Everyone does.

Set a low daily budget $2-$5, and a high CPC to start with.
Leave it for few days, after you get a good CTR, reduce CPC and increase budget.

Choose highly targeted keywords and a relevant landing page.