You can also pack with a rolled up sock -- it might be a good idea to do this before buying something just so you get used to the feeling of something in there. Some guys find they don't like packing, so it might save you the money. Socks are also super washable and don't look suspicious if someone finds one in your drawer...
Also like Elis said the mr limpy is the cheapest. I got one on amazon, but there's a lot of other places you can get them.
Most STPs are quite expensive, but there are a few cheap options -- they're just less realistic