When I began building my first KAP rig (Picavet) I was somewhat shocked at the price of the little pulleys other people were using. The Picavet rig requires 4 single pulleys and two double pulleys. I ordered six small commercially made pulleys from a model sailboat supplier at a cost of about $8 each. This was by far the most costly component of the system aside from the camera and possibly the kite! On top of that, I believe these items were out of production all together at one point.
I wanted to find an alternative so I wouldn't constantly be stripping one rig of it's pulleys to use on the next. I began my search by visiting hobby shops, where I was rewarded with a variety of blank stares and dumb looks. Next I tried the hardware store. They actually had quite a variety of small pulleys, but none as small as the sailboat pulleys. They also had a few other things that might be made into pulleys.
After acquiring a small collection of alternative devices, I wanted to compare them in some objective manner. The picture below shows the relative prices and sizes.
As you can see, there's quite a range of size and price. The hardware store pulley was the only one that was obviously too heavy to consider.
Next, I wanted to see if the jeweled-bearings of the sailboat pulleys imparted some magic quality that I might lack in an alternative. I decided to try and measure the resistance required to start the roller moving. My method was to balance a piece of string about 18" long on the pulley, 9" hanging down on each side. I then added paperclips to the right side one at a time until the string began to move. The results are shown below:
The results were repeatable, plus I experimented with both heavy and light twine. In every case the winner was the big nylon "screen door roller". Second best was the sailboat pulley. The "chain link" seemed promising. I believe it's supposed to have some sort of bearing in it too, but it didn't really do well.
"Screen door rollers" are sold in pairs as a replacement part for the kind of aluminum sliding screen door used on porches and patios. It can be found in the storm door parts section of the hardware store.
It's too late for this rig, but next time I'll try these and see how they work out.