Sears 10" Digital laser level #48292
$46.00 with tax and shipping (special price $10 off on-line)
1" x 36" Aluminum angle stock from Lowes $9.95
SS Washers $1.20 (only need one)
1/4 thread 1/2" bolt (my stock) probably 25 cents
Vinyl cushion pads $1.20
Two AAA batteries (not included, I had at home)
Total Parts: $58.60
This is not my idea, but I saw it some time ago on another forum and it looked like a pretty good solution to the "professional" option from Longacre and others, and it's quite a bit less expensive.
Measure your wheels across the greatest diameter. My 19" M220 wheels are 20 3/8" and my track wheels are 20 1/2" so I cut my angle stock at 20 1/2". You don't want to go too long or you'll interfere with your rubber.
Then measure the midpoint of your shortened angle stock and mark this. Then you'll need to measure from the side of the digital level to the middle of the threaded mounting hole on the under-side. Transfer this measurement to your angle stock, mark and then drill a pilot hole to make sure you're on the right track. Drill out with your 1/4" drill bit and deburr the hole. Then put a washer on the bolt and mount the digital level to your angle stock. Tighten the bolt put the vinyl pads on each end of the angle stock that you will be holding against your wheels to prevent any marks and you are done.
If you are okay subtracting the measured angles from 90 then you'll be set to read your camber. You could zero the digital level at 90 degrees but I think that just risks introducing more error. This is probably only accurate to 0.1 or 0.2 degrees but for my use this is just fine. Make sure you use even pressure in the middle of the gauge and don't push too hard as the cushions on the end can compress and give you an error. If this is a problem I might just put some thin felts on either end but it's easy enough to do by feel that I think it will be fine.