I assume you are talking about a wheel steering system? I have several friends who have done this and I have worked on a lot of these systems. Also, what size boat are you looking at?
If you look at some of the more traditional boats, they have very simple and easy to build steering systems. For example, the pinky schooners used a great big tiller with a line
going to a block on either side. The line
then lead to a drum which had several turns of the line
on it and is directly attached to the wheel. If you have the space for this setup and can do some basic woodworking, it is probably the easiest route to go.
Another relatively easy to put together system that does require purchasing some parts is a worm gear setup. Places like the lunenberg foundry still make these. You order them by the rudder post diameter(they are made for wooden rudder posts).
If you want to go the quadrant route, you could easily machine your own parts. If you have access to a mill and a lathe you could make everything minus the pedestal for less than $100 and a few hours of time. If you wanted the pedestal to look good, that would take some real work although it might not be too bad if you built it of wood.
I have also seen some homemade jobs out there that are less than ideal. Many of these actually have the control lines
leading from the transom to the aft edge of the rudder so they pull it from there.