|I'm with wanderer on this, you need to provide more detail.|
If you're planning on feeding 3 separate buildings it's important to know how far apart the buildings are, how you plan on interconnecting them. Ideally, if you had internet at all 3 locations you would use a VPN.
But since you want to run all 3 throug one internet connection then your options change. You could use wireless point-to-point shots between buildings or you could use dedicated fiber optic lines between buildings. I can't think of any other viable options for interconnecting the 3 locations.
Considering you have limited money I would suggest you seriously look at putting separate internet connections in each location. Then buy SOHO router's that are capable of being VPN endpoints and setup a VPN between the 3 sites. That's probably a lot cheaper than buying the necessary wireless p-t-p hardware and is definitely cheaper than leasing 2 dedicated fiber optic lines.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.