switchplates?
Answers:
Home Decorators catalog or online. They have volume discounts, decent quality and beat the prices of both Home Depot and Lowes in my area.
Other answers:
wal-mart, lowes, home depot, k-mart
wal-mart, lowes, home depot, k-mart
My personal choice would be HD or Lowes. They will be plated most often in your defining of Cheap.
The cost to shop and ship, even online, is very likely no different in the big picture, than actually going to a Home store.
Rev. Steven
I like bouncing between Lowes Menards and Home Depot-they like to compete with each other so you can't expect one store to be the cheapest on all items. You just have to watch them all. I've had the best customer service at Lowe's though if thats a factor.
Brass is not cheap no matter where you get it.
I would try your local hardware store, as they will likely have brass, then most big box stores. Brass is not an everyday item, plastic is. A local hardware store can order it for you, if that is your preference, or an electrical supply store.
Jesse
I would take some time and shop some secound hand shops. You can get some beautiful antique brass fixtures for pennies. Many people redo there whole house and donate the whole lot. But you have to have the time to shop around and most people don't have it. I got some really beautiful vintage brass door handles a while back and with a little brass cleaner they were beautiful.