Adding PS steering has been an often discussed project here on TBN. Adding an automotive style PS pump is usually an issue due to lack of space. Using the tractor's hydraulics and an orbital steering valve and proporting valve is slick but expensive. In either scenario, you then have to still engineer the cylinder mount/tie rod aspects and hydraulic plumbing after that. The kits offered by Rick Davis at TPS are as cheap as just an orbital valve alone and very easy to install with basic tools and mechanical skills. Not as slick as OEM PS but just as functional and as easy as it gets. Using automotive style parts and shopping around the net for a steering cylinder etc could be the cheapest route but it will involve the most skill,time and work and is ultimately dependent upon whether there is even room for another belt drive accessory to be driven off the crank pulley. I personally love engineering my own things and shopping for value priced components but frankly, the TPS unit that Ductape posted about is hard to beat in my opinion.