I second this. You can just buy the MFJ933 and add your own metal for the loop. I used copper tubing from the plumbing supply store, and I can clamp in different lengths that are optimal for different bands. The MFJ933 is $190 for the box and it will happily run 100W. I think that's the closest you need to get to "buying" a loop. That being said, you never want to run anywhere close to 100W indoors. At 100W the currents on a loop antenna are big and hazardous, and the fields are strong enough that you don't want people within at least ten feet of the loop. Even running it outdoors you have to be careful, because it's close enough to the ground that some kid might walk up to it.