What i do when i don't have much money to spend and still want to get lucky to get some money on slots is this:
Calculate your income and spending. Never go below.
Have a buffer in real life and never use that buffer for gambling.
When you know you can bet 20 euro a month, put the casino to max deposit 20 euro / month
Cash out at 3x your winnings ( so you win an extra month ) and still get some extra cash in your pocket.
Don't get greedy!
My tips do what you want with them.