I got something similar to this at a craft fair recently, and I just love it. It's much easier to find my keys in my bag now, or If I don't want to take the bag, it slips easily onto my wrist. This one is for my mom. I 'd guess it cost about $3 in materials, but I already had most of them on hand. I spent $2.50 to get the hardware at JoAnns, and it comes in sets of two.
Tutorial at the always awesome U Create. I'd suggest adding maybe an inch and a half to the strap than what she suggests if the person you're making it for doesn't have small wrists, otherwise it may be tight to get past the hand.