The cost of waste associated with air shaft systems will be tough for you to manage. Jeff has valid points as to not considering draft at all.
Today though, the technology and designs for glycol systems exist that can preserve the quality of your draught products from the keg to the glass the life of the keg. There are retailers who make a living just on their draught sales alone by utilizing these systems.
If up front cost of a system is an issue, ask the installer if they are associated with a financial organization who can offer you programs to spread out the cost of the system. If they are not, call our customer service number and have them provide my number to you. I'll provide contact information to you for this type service.
Scott Zuhse, Instructor
Micro Matic Dispense Institute