Variety and versatility are the key decor aspects of throw pillows. As you shop for decorative throw pillows, you deserve to find them at a price your budget finds cheap, and yet you should be able to find throw pillows that do not seem cheap.
Also, as you shop, remember that we get what we pay for. Sure, you can buy low-low-priced throw pillows -- for a few dollars -- online. Just really consider if what is being offered is made of material that is durable, and that you can rest your head on for a nap sometimes.
The best, cheap throw pillow is one you actually want on your bed or sofa.
Online, Overstock.com has "a ton" of available decorative throw pillows -- with some sold for under $10. Be sure to check there, as you may find the "just right" throw pillow at the "just right" price.
Offline, I definitely recommend a stop at Goodwill for savings on throw pillows. While there are -- regularly -- donated throw pillows on Goodwill's shelves, I have recently seen new ones for sale there, too.
You would also do well to scope out yard sales, flea markets, and similar situations for throw pillows. Just be keen to the fact that items sold in those settings will likely have seen quite a bit of use.
Of course, eBay is full of throw pillows for sale by auction. There is some savings to be had there. (See the eBay section below for possibilities.)
All the best to you in your economical throw pillow shopping!