Your solution in good for the 100's of feet so not going to cut it.

Since there is no line of sight, you'll run afoul of FCC regulations. So the best solution may be a tethered phone. Here I can use a Virgin Mobile android phone (99 bucks at target.com) and it's 35 buck a month plan plus Easytether for 15 bucks. I'm done.

NO LINE OF SIGHT means no good cheap solution.

Why isn't internet service an option?
Bob