For those who think you can make a cheaper jerky at home; it's quite difficult. I own a slicer and a weston horizontal machine and after all the effort and minimal cost savings, have reverted back to store bought. What's already been pointed out, when all is said and done, you only yield about 33% of the original roast. So a 10lb roast will yield 3.33lbs of jerky.
With Jack Links, while they sell formed strips and nuggets, the majority of their products are whole strips. To make whole strips at home is going to be the most costly. Also eat/make a lot of it, you're going to be doing a lot of slicing and will need to sharpen your knife often or you can invest in a slicer...When you deal with large roast, there's going to be some unused trimmings.
If you're okay with the jerky gun and using hamburger which is a much different but less costly product you have another factor to worry about, pink slime. It's still around so if you don't want to eat that, then you need to do your homework and you may discover that the great deal on hamburger you've been buying does indeed contain pink slime.
Now there's the ingredients/spices, obvoiusly they're not free and if you buy in bulk you will save more. Most recipes calls for marinading the meat in Worchestershire or Soy sauce. One problem with that stuff is it's smell soaks into your hands, so you either live with the smell, buy gloves or you need to scrub your hands with a slice of lemon to get the smell out. Next with the odor, obviously your kitchen or possibly the whole house is going to smell like a meat locker. Then there's effort and small expense of clean up and the electricity used to create and clean whatever equipment you use.