I don't think AMD ever made a 2400+ Palomino chip, only the Thoroughbred version is available (I stand to be corrected!).If I am wrong, you will need to make sure which of these versions will run on your board.
You are correct about the manufacturing process being the smaller architecture. A by-product of this, is the chip will run slightly cooler, as the core voltage is less.
A quick review of your motherboard suggests it will support a 2400+ processor, so by inference, the Thoroughbred is the chip for your board.
I am puzzled about your "price difference". Where have you found a 2400+ Palomino?
Any performance difference will be negligible. The processor manufacturing process, is simply all about getting more transistors on a smaller silicon wafer, hence reducing manufacturing costs. It has nothing to do with performance!