That's way too high, but it depends a lot on where you live (and experience level). Network Admins that I've known typically make 30-50k / year for a network as small as 100 computers. Network Admins at very large corporations (like Coca-Cola or something) can make more, in the 50-80k range, but you need experience, and you're dealing with a much more sophisticated infrastructure.
It's very easy to outsource a lot of administrative functions these days, so keep that in mind when searching for a job and negotiating salary.