I got a bodyfat scale, they cost about 30$ at Wal Mart and I have skin fold calipers I got for 8$ from a SPorting Goods store, but I don't really know how to use that very well except for the one site on the obliques.
Your body stores fat for a reason, it's just flat out dumb for an athlete to go under 5% body fat. If you do any hard core exercise and you don't replenish properly near that borderline, it does way more harm than good.
Michael Jordan and Bruce Lee had lower than 5% body fat. Bruce Lee had VERY LOW body fat.