Server that will handle SBS with 7 users and a decent tape backup: $3500
Backup software $700
Server Antivirus software w/ email protection $750 (Don't even CONSIDER running exchange without server-level virus protection!)
anti-spam $500
SBS Licenses $2000
Remember you will have about $1000 per year re-occuring expenses for AV and tape backup software...
Every 3 - 4 years you will have the microsoft licensing upgrades at $2000, probably needing hardware upgrades at the same time.
Switch $100
cables, ends, crimpers... really depends on the distances... 1000 Ft. of cable is going to run around $200, depends on if you have to run plenum cable to meet fire codes or not... could be more, could be less.
What will you actually be doing with SBS? What services are you interested in? Just file sharing and email? If you need SQL, add about $1000 to the licensing.
If you are just going to do file sharing and email you could also go Linux:
Server with tape backup to easily handle 7 to 25 users:
$2000
Server software: Free
Backup - included
antivirus - included for email (clamav/amavisd under postfix)
anti-spam - included (dspam or spamassassin)
Yearly licensing and upgrades: Free
switch $100
cable etc - as above
You could pay someone $1000 to set up the linux email/Samba etc and still save money.