As a recreational gambler, I look to do two things: feel the rush and not sweat the losses. If you're betting $1, you probably don't care about winning or losing, so why bother? If you bet $100, you should keep more than $100 on hand, because you won't be able to bet again after a single loss. So, you budget for gas, food, rent/mortgage, etc., right? So budget for recreational gambling.
A couple of rules of thumb: as a recreational gambler, you'll lose about $5 on average (betting straight ATS, o/u, or ML) for every $100 bet. BUT your win/loss ratio can be several times that, so maintain outside cash flow in your budget until your "luck" changes. Enough to cover (sorry, I have to get mathy here) about 3x the square route of the number of bets you place, or enough to cover about 10 consecutive losses, whichever is greater.
And if you're still reading, one more word of advice or two: If your losses exceed the numbers you budgeted, take a break. This is for fun, right? If you overextend, it ain't fun any more.
Now, brace yourself. The Kelly crowd may stop by with formulas with Greek letters in them.