its according to what your selling
In his store.
spend a lot of money
Buy it from Nook....eventually.
You can't.
Tom Nook and the Mayor
You need to get 5,000 Nook Points.
On some days in Animal Crossing Tom Nook will say he's having a sale where you get 5x the points you usually get
you have to wait until nook has it in the store
balloons or point tracking system at nook's
This feature was only in the original Gamecube version of Animal Crossing, and is not accessible in City Folk.
the most expensive things
You can get a fishing pole at Nook's store. Then he will tell you how to use it.