I've got a whole stack of CDs that I apparently mis-treated in my past. Short of sending them to some company for re-furbishing, or buying one of those grinders for $100, is there any method, or cheap product that will fix these? Some skip, some stop, some the machine can't even find the starting track.
Any help is greatly appreciated.

Look under your sink, or in your bathroom cabinet.

Car wax/polish can work, especially with scratches that go from inner edge to outer edge. Just rub a small amount of it into the scratch. Or try some ordinary household polish.

Or you could use something like baking soda (white not the blue gel) toothpaste for scratches which go 'round' the cd. It's quite abrasive and if you rub it over the scratch it will wear down the plastic around it so the scratch can't be picked up by the laser anymore. Just don't go right down to the foil.

They are ways I was told of and they have worked for me on lots of occasions. Another way that was suggested to me, but to use as a last resort was to colour the whole CD in with a blue marker pen. The darker colour would help to cover the scratch up. But this is a bit risky because you only get one pop at it and it might not be read by some CD players. The other two methods you can progress with.

Sorry it's a 'touch and go' suggestion but if you don't get any better ones, then it's got to be worth a try. At least on a less important CD.

Over here I’ve seen some CD repair kits, which through some treatment process, cleans the CD and fills in any scratches. I’ve been tempted to buy one, but there are around £20+ and I don’t want to fork out on some gimmick I might be getting hoodwinked over. Anyone use one of these before?

Ok, for anyone else in the same position as I am with a bunch of dead CDs, I found a site - 303sonicblast.com - good company name (tops in car care products and chemical engineering) they were actually offering free samples of their Sonic Blast CD Repair. I requested one, it got here in 4 days, tried it on a CD and I couldn't believe it .. it worked perfectly. So, I grabbed the little sponge-thingy that came in the foil sample package and eeked out 4 more discs worth of repair - every one of the played great.... even the one that my machines couldn't even find the starting track info on. One disk, I must admit, had some gross damage in the center, the Sonic Blast made it playable...but you could almost hear a "digitized effect" if you listened super hard. Great Stuff, Great Price - like under $10 for 300 treatments, and damn, it really works. Anyone else used it?

To fix scratched cd's simply place the cd in the freezer for say 30min. After you remove it wipe with some kitchen roll. You may think this is stupid but it is proved to work. Got this tip from Future Music mag years ago.

Got lots of cd's working this way, try it!