A lot of guys also use those mats you put under your sleeping bag. Voodoo imports mostly good stuff. I have a US Peacekeeper, but I don't remember using it. I just like getting dirty.
I have an extra thick foam military surplus mat if you want?....I bought the midway competition mat for like $50. Thing is very well built and have used it for various classes and range time and works perfectly.
My favorite shooting mat for Appleseed is an old area rug, lol.
The thing about a lot of mats is that they aren't wide enough to fit your whole body on when in a proper prone position. There are exceptions of course. Also, many have a slick PVC type coating on the parts where your elbows and knees touch the mat, which causes them to slip around and makes it harder to build a good position.
I suppose the upside to an actual commercial shooting mat is that it will usually have a nice handle and shoulder strap, making it easier to carry.
I have one of the rifle cases that opens up into a shooting mat -- I believe its the Voodoo brand. I don't use it as a mat anymore because I tend to track dirt and dust onto my mats... not stuff I want inside my rifle case.