One of my favorite ways to buy inexpensive things for my daughter is through consignment sales. There are many consignment businesses open year round as well as organizations that do sales on a yearly basis.
My favorite, and the largest that I know of, is in Birmingham, Alabama. It's called Kid's Market. It is held biannually and is housed in an old grocery store. You can sell your child's old items and you can buy new ones.
I like to look for toys, bedding, books and clothes. Kid's Market has strict rules on items in working and good condition so you almost always find great items in great condition for great prices. At the close of the sale items are sold at 50% off which makes many items practically free. Try selling old items at these sales and if you are unsuccessful you can then donate them.
Check around for consignment sales in your area. Also look for Mother's of Twins sales, double the stuff for half the price! You can save and make yourself a lot of money.