The people behind these scams have to use legal services as well. They do have to pay in some way for each letter that goes out. There's definitely a "sweet-spot" in the pricing which maximizes the ratio of intake to expenditures. I would bet that they and other patent trolls have found that sweet spot long ago.
I was under the impression that some of these patent trolls are really just a collection of lawyers. If they're doing their own work, instead of getting an outside firm to do it, their costs should be much less.
I've long had the opinion that situations like this (as well as Intellectual Ventures) are the lawyerly version of hacking. They're just trying to find free lunches in the system the same way that MIT computer heads 50 years ago were trying to disable timeshare accounting for their usage.
By defining costs that way you do bring down the overhead, i.e. what they have to pay up-front, but not necessarily the actual costs.
If I am a lawyer doing my own patent trolling, and that takes up 10 hours of my time that I could otherwise have sold to someone for $x/hour, then $10x is a cost associated to the patent trolling, even if I didn't actually have to transfer that money to someone else.
Even so, if they hit up the victims for $100 instead of $10000, they'll need to send out far more letters, and deal with far more targets who simply ignore the letters. IANAL, but I believe it does cost money and time to actually file a lawsuit and/or compel the targets to do things like pay up under penalty of law.
Note that in the majority of cases, they don't file a lawsuit. Their business model almost certainly depends on that. You're right, of course, that their volume would have to increase, but I'm not ready to immediately dismiss the notion that their current tactic is not the most efficient.
