A GREAT way of saving money on stamps is to carve your own. If you want all sorts of textures for your art work, just carve your own. I find that the little erasers you can stamp out of are too small sometimes so I really like making a stamp that shows texture with the styrofoam meat trays. They can be at least 12" long so you get a great huge texture on your paper.
Michael's sells an economical way of buying a stamp kit including a breyer, a tube of ink, the stamp carving tool, a tray to put the paint, and a piece of rubber to stamp into. If you use a coupon, you get it for so cheap it amazes me. I mean a big savings. Just a breyer is $16.00 and the tube of ink is $7.00. The piece of rubber to carve is $6.00 so when you keep adding everything up, it is alot of money. The box at full price I think is around $34.00 with the coupon $17-20 depending if your coupon is 50% or 40%.