Check to see if your local Lowes has a 'loaner' bin for trays and those black pots. Ours does. It's run on the honor system - borrow what you need and please return when done so others can use them.
Rural King has cheap trays (dollar and change each and a good size). They are only in certain parts of the USA though - Florida just got its first two stores. If you have one, check out their prices. Better than Walmart in most cases. They also ship.
http://www.ruralking.com/