I want to use a bow and arrows as my LARP character's weapon, how many arrows should I buy, minimum?

I'm considering doing LARP soon, and I want my character to use a bow and arrows as her main weapon. I am considering a combat knife as a second/back-up/close combat option. My question is, how many arrows do I NEED? Let's admit it right now, I'm not rich! I don't want to pay for 12 arrows at $16 an arrow! Please help!