The pay can be really good depending on each specific contract. I usually end up doing audits for at&t. It is supposed to be 100% tie off, a cable runs vertically the length of most towers and your cable grab is attached to your chest. It slides up at any rate you climb and will descend at a pretty good rate also. IF you fall or slip it grabs the cable and smacks you in the face. When you get up top you attach a retractable lanyard to the tower and do your work. The harness weighs about 50 lbs, it's a great workout if your not trying to consume more calories than you burn
Climb, drop a tape weighted tape from the top, measure the tower and the height of the antennas, take some pictures, diagram the coax and specific equipment model and serial #s, and climb down.
A typical 200'- 400' tower takes about 45minutes to 1.5 hours. I contract my own work at a rate of $150. per tower. On a good day, even in the dead of winter, I can climb 6 - 7. Mid summer of you don't die from exhaustion 8 - 10 is a great day.