You can start with renting about 3 refs when you have a balance of $1. See if they are earning a profit, which they generally do. Use the profit to purchase more refs. In some time, you will be in a position to get bigger ref packs.
Note: If you have some money in your Paypal or Alertpay balance, pump it in immediately. Atleast $5. Because then you will be way ahead of your schedule. Atleast by 4-5 months.
Happy Earning. And always keep some amount just in case you need to recycle. And always keep an eye on the expiry date of refs. Don't but new ref packs and exhaust your balance when other ref's due date is near. Else you will lose them!!