I got a single 3" tower from someone who upgraded to a triple for free, and then bought a 2 tap tower addition on E-bay for $15. Scrounge around your brew club buddies, you might be suprised what is sitting in the basement/garage/attic. My triple tap conversion is shown here:
PS. If you are interested, I have three used 4 tap tombstone type stainless steel towers with built in drip trays that I will let go for $20 each 2 of them have one broken shank each the third is complete. These were taken out of a bar that closed in Boca Raton Fl.