I think you're getting a pretty sweet deal with board, actually. You might also consider the cost of a vet visit in a boarding situation (where the visit fee is most likely split amongst several people) vs. you paying the entire fee for your (one) horse.
My Mom has about 20 acres for our horses to roam on, and it's still a pain in the butt to manage everything. You spend more time and money dinking around with faulty water tank heaters in the winter, electrical cords, fans, hay, feed, etc. than you would in a boarding situation. Before she invested in gigantic steel stock tanks (which aren't cheap), we had to chop ice on the pond at least once a day, preferably twice. And with the snow thigh high, you weren't driving to it! Moving big round bales during winter is a pain too.
Having your horses at your own place is great, and I really love being able to watch them roam freely at home, instead of getting daily "turn out." It makes me happy to see them happy. But you really have to sit down and analyze every little cost to get a good idea of how much you're saving by bringing them home. And always do worse case scenario! I learned that the hard way. :(