Fittingly, Germany has a federal office for protecting the democratic state against nazis and other threats to democracy. Each of the sixteen states also runs a smaller effort of its own. Some have dedicated organizations, some locate the work within a ministry, but all do something.
Because of the variety it's nontrivial to add up the cost of all this. I added up six of the biggest organizations and that came to €220 million, so I blithely estimate a total of €250-300 million.
Conveniently, there are 25-30,000 nazis in Germany (says the LfV Hessen), which means that the state spends €10,000 per nazi — or would if all the work were directed against nazis, which it isn't.
Browsing the annual reports gives me the impression that the resource are divided mainly between nazis, leftists and islamists, with a little for other purposes. Since the nazis do the bulk of the killing (more than 90% since reuinification, exact numbers are subject to discussion), but the leftists and islamists get the bulk of the political attention, I simply split the resources evenly: 30% for nazis, 30% for leftists, 30% for islamists and 10% for randoms.
In other words, nazi surveillance costs something in the vicinity of €3,000 per active nazi per year.
Something odd happened recently: Two nazis called Uwe Mundlos and Uwe Böhnhard committed suicide for unknown reasons; a third called Beate Zschäpe then blew up the flat in which all three lived.
The police afterwards found evidence there that the three had killed about one Turkish immigrant per year for the past decade, scattered all over Germany. The newspapers write they may have had local assistance in many/all of the locations, and they made a DVD bragging about the killings. I have no idea how widely it has circulated. (A search for
dvd paulchen mundlos may locate a copy.)
Anyone who's helped the killer trio, anyone whom they have approached for help, anyone to whom they've given or sold that DVD: The state has spent an average of €3,000 per year watching each of those people. And it has not discovered either the DVD or any of the requests for help.
From this I infer that if a capable, well-run state such as Germany is to carry out widespread surveillance of its citizens, and do it well enough to catch someone like the trio Mundlos/Böhnhard/Zschäpe, then it has to spend more than €3,000 per year and potential recruit.