If you decide to put one together yourself, I would not recommend buying used equipment off e-bay. I did and spent just as much money trying to cure my foam problems with used equipment as I would have if I bought new equipment from a reputable source. I finally fixed my problem by buying a tower from Micromatic. After I installed the tower and everything worked perfectly I looked inside the old shank I bought used and saw if was very rough inside causing turbulent flow and foam. So if you can't inspect used stuff thoroughly I wouldn't fool with it.
To answer your question, my system is a old freezer with a temp. controller and a double tap tower. It's not a lot of work, the quality is good enough for me. The only drawback I see from my system to a store bought system is top loading the kegs. I would think a front loading system would be better, especially in a bar setup.
Good Luck!
rr007