is it cheaper or more expensive than a linux server?

I think you need to clarify as to whether you are talking about a shared hosting account or a dedicated server, but in either case Windows is usually more expensive and not as good as Linux.

While I'm generalizing here, usually Windows-based hosting is more expensive, for a number of reasons:
1. Software is far more expensive
2. Requires more maintenance
3. Upgrades often cost money

shared account. i think i mentioned that in the subject
how much does it cost per month.
a friend of mine is paying 600$ a year and it seems a bit expensive for only 10mb hard drive

$600 a year works out to $50/month, or thereabouts, which is rediculous for a 10 meg hard drive. You can get a virtual server for $50/month, with a 1 gig hard drive, lotsa ram, full scripting, and everything... .

Windows hosting are generally more expensive for several reason:

- Windows o/s is very expensive
- higher hardware requirement
- higher maintenance cost
- 3rd party software usually cost more in Windows