When we got ours we spent about $4 per theoretical watt, which is much worse than a farm's theoretical watt since they are able to position them better and in some cases even adjust them throughout the day, getting much closer to capacity.

If you look at a solar installer's cost breakdown, the actual panels aren't nearly as much as you'd think. They spend a lot of overhead on sales and other stuff. Installing them on flat land in much larger quantities allows you to minimize overhead so that your primary cost is the panels themselves.

The two advantages of a home installation are: you already own the land, and very little transmission loss (mostly with the inverter, I believe). Those aren't enough.