There is a mac MINI update coming soon. See here.
You might find this will drop the price of the existing ones. If you're feeling flash with cash I've seen apple resellers (who else could it be?) selling new outdated models of macbooks for about 1/3 less than their list after an update on ebay. Maybe the same thing will happen for mac mini's if you watch.
Be careful of one thing - the combo drive doesn't write DVD's. This could be painful. If you think it is get the one with the combo drive.
I wouldn't worry too much about the software costs. I've been using them for years now and never bought anything other than ilife. If you need professional editing stuff you will pay.. but you're getting serious to do that and I can't imagine you would need that. They do normal "home" video editing great with the standard stuff. Don't forget you won't have to buy anti-virus or spyware programs.

