$50 is not a lot of money, especially when you're considering using it to gamble with and potentially lose.
Regardless, let me entertain that notion. Personally, it takes me 90 minutes to get to my 'local' casino, one way! So I won't be making that drive with a $50 budget as it would cost that much to get there in gas, haha. The simple answer is that it should be whatever you're comfortable losing! So let's say you only have $500 for a weekend or $50 for a day. People often ask me what their budget should be for the casino.