Oh! You have to pay off your second mortgage (the one for 38,500 bells) and then the next day a tortoise named Tortimer will talk to you in the entry-screen thing where Isabelle usually is. Then, the day after, if you go down to the dock-thing, a boat will be there, and you can go to the island for 1,000 bells.
The villagers don't really donate at all. They'll put in a few hundred Bells here and there, but nothing really big. 99% of the funds are going to come from you.
Here are some ways to make quick bells.
Shake the fruit trees and sell the fruit at Re-Tail
Pick up shells on the beach
Go Fishing
Catch bugs
Dig up fossils
You make me glooooow, but I cover up, won't let shoooooooow, so I'm puttin' my defenses up, 'cause I don't wanna fall in looooove, if I ever did that, I think I'd have a Heart Attaaaaaaaaaaaaaack~