Anyone telling you that you have to pay is a douchebag. It's very easy to do. First you bypass. If you don't own Resistance Fall of man I'd use the patch blocker. Then you download your CoD 4 save onto a flash drive. After, you change the inside of the files (easy as copy and paste) and plug it back in. At this point you replace the CoD4 save, delete the patch, turn on the patch blocker and voila hacks! This is a very rough tutorial and definitely look at some of the other tutorials here.
Rep and Thank if I helped