SBS CALs certainly have to be considered. SBS CAL licenses are about $100 per client. While that adds up, it's STILL no worse than than the cost of Server 2003 CALS plus Exchange CALS. And, if you ever need SQL, the CAL cost advantage gets even better. ALSO, SBS automatically gives you CALS to all added Member Servers in your domain. If you add another Server 2003 or two, there's NO additional CAL cost.
SBS Premium Edition has been less than $1000 at Newegg. If you buy Windows Server, Exchange, ISA, and SQL separately, you're talking thousands of dollars more, PLUS you STILL have to buy CALS. And it's pretty easy to argue a signficantly lower maintenance cost with SBS than with non-SBS Server.
As always, each customer has to consider their needs/wants/technical abilities and consider what they are getting for their money. I'd argue that paying, maybe, $20-$30 per employee per year for full remote access, automated reporting and backups, licenses to SBS, Exchange, ISA, and SQL is a pretty good deal.