As I suspected, some folks (based on feedback on the blog and email to me), made some points about cost - specifically, saying that SPS is too expensive.
Above and beyond the points I made in my quite lengthy blog entry, fundamentally, you must ask yourself - "what exactly do you want to do today and where do you want to go?"
The first, obvious point that I didn't mention in my most recent blog entry in the TCO section is that Windows SharePoint Services (WSS) is part of the Windows Server value. What this means is that there's no additional cost of using WSS above and beyond the cost of Windows. So if all you want is a collaboration solution for groups and teams, then you can deploy WSS.
If, on the other hand, you are looking to build a full partner, employee or organizational portal, then purchasing SPS is worth the money. Granted, I am biased since I work for the SharePoint/CMS team. (but I wouldn't be working on the team if I didn't think so.) It's all about Build vs. Buy. That's what the question fundamentally boils down to. SPS provides Search, Targeting, SSO, My Sites, Site Directory, Navigation and much more - features that are consistent with aggregation that every Portal requires. Building your own solution, while entirely feasible, can be very expensive - it requires architecture, great development skills, testing and dedicated support. In short, you incur a lot of long term costs on developing and maintaining your platform vs. focusing on your specific development for your business problems.
I have seen organizations that choose building their own Portal with ASP.NET. While that's definitely a viable option, it again, depends on what your end goals are. If what you really need is an enterprise portal (functionality that SPS provides) and you end up developing everything in SPS, custom development will cost you a great more than using SPS; needless to say, a custom developed solution doesn't give you the upgrade you would get with SA.
As for specific issues around cost, you should think about purchasing core CAL that bundles several product CALs. This can minimize your overall software costs.