If it was just a resistor, $1 is too much ... there are some out there that consist of real plugs, just as used on the transmission, with isolation etc. The plugs would warant a bit higher price than $1 ...
Apart from that, !CAGS is pretty easy to install, especially if you can put the car on a lift ... didn't he get some kind of install instructions with the kit?
Here's a link to install instructions for either a
finished cable or just a
resistor solution ... not too much you can do wrong except put it in the reverse solenoid plug ...