The minimum amount you have to deposit into your account to start playing at most casinos is between 10 and 30 dollars. Some casinos offer a possibility to start a real slot game for free through so calles free spins.
Not all casinos are clear about this. But do you want to play responsibly? Then impose a daily limit yourself. Make clear agreements with yourself and your partner and write it down. Only gamble with money that you can really spare and never, ever! go over budget. Gambling should be about fun, not about debts or trouble. Want to know if you are a responsible player? Check this.