We all have a friend who constantly hosts home parties for Pampered Chef, Tupperware, Party Lite, jewelry, but purchasing items can be expensive. A few years ago I decided to stop attending these. But if you host these types of parties yourself, it is good manners to reciprocate.
I usually respond with, "Thank you but I'm sticking to a tight budget this year and saving for _______."
You will often be asked to attend anyway to make up the numbers, but if you attend one, you'll have trouble turning down others. Unless it's a product that you like and want to purchase, it's best to refuse if you're trying to cut down on costs.