$275 for that setup with configuration is a pretty good deal.  If I were doing it for a customer (with install) I'd be closer to $400.  The reason you're still getting service through the corn is because its 2.4ghz.  It's the same frequency that the majority of your indoor wireless devices use and it can penetrate walls and vegetation fairly well.  I bet if you were to speed test the link in the summer it would be much slower than in the winter due to the vegetation.  Evidently it is still faster than the internet service you are subscribing too!  If you were using M5 radios (5ghz) you're link probably would work right now as it can't burn through vegetation.