For most, the new options probably will reduce costs--contrary to the analyst reports you're bound to get within the next few months showing it's more expensive than Windows.
If your costs are mostly wrapped up in desktop/server software and maintenance, it will save you a large percentage of your budget.
If this were any vendor other than Sun, I'd question its ability to deliver. But Sun has a long history of delivering software that is both fresher and more stable than the industry norm.
If you're feeling the crunch of budget restrictions, look into Sun's offer. If you have some time, wait and watch. If this works for Sun, other companies--even some large ones--will follow suit.