RE: servo controller thats voltage based
The Contraption you Linked to is a PIC Controller Circuit.
It is a Programmable Micro Controller. Not very expensive at all for the components, which you will find at any electronics Parts House on the internet....You can BUILD it for much Less.....but....
You must be able to write the Program and Compile it. (There is Software for that)
Then you Program the Chip with a EPIC programming Board......
Cost of the Software is around $99. (You can spend a LOT more, but its is not necessary for this basic stuff)
Cost of the Programming Board is around $70....( same as above, go cheap.)
Now you see why they charge you so much for the Completed contraption....Lol....
If you are interested in pursuing this, I recommend the Following Book to get Started. It details all that I have said, above....