Somewhere around $500 - $600. Per year support contracts are around 20% so the life time value of a customer is probably around $1000.
And since my replies were being rate limited, I'll respond to your long-tail question above. We have tried a lot of long tail keywords, but they have such low frequency that Adwords penalizes you (low quality score) for using them, which means you pay more per click account-wide. That is why I say get to know Adwords - there are a lot of gotchas.