1. Figure out how much money you would need.
2. Calculate the price of a monthly card that would give unlimited skating for a month. It should break even at about 20 day tickets.
3. Divide the amount you need by the price of a monthly card.
This is the number of cards you need to sell to get funding for your rink.
4. Sell the tickets, but don't collect the money yet. Tell them that you will only collect the money if you reach a certain level of ticket sales. That will encourage them to spread word of mouth to their neighbors. (If they aren't enthusiastic about an ice skating rink then you are building in the wrong community).

5. Also tell them that if the sale happens, you will give them a free T-shirt when they pay for their ticket.

This method has the advantage that, not only do you get the money without borrowing and interest, you also know that you have customers. The only out of pocket expense will be the T-shirts.