If you've written a addon for WHMCS, then the script from the original post is pretty easy to get going. I ended up removing the price adjuster since that was not working the way I thought it should. So now I just have this module update the year 1 domain listings. The script can update the other years as well if you click the check boxes but instead of just using the prices from eNom it multiplies the year and the year 1 price together to get the year2,3,4,5,6 etc. prices. (Weird)
I too originally I had looked at the eNom plugin but decided that was too much money for a plugin that I only needed one feature of. Next time try calling their technical department. I've had better luck talking to them on the phone than I have using their ticket support system.