I agree with the above, for 400 dollars you might not get a lot on that list, or it's definitely not going to last you a very long time and might end up spending way more on other upgrades and repairs.
I'm also looking for a new MTB but just had to realize that I'll have to spend some money to get what I want. I'm building a road bike for the moment and yes, all counts up. Even small things like cable stops etc. You'd be surprised how much you need when you're building a complete bike and how much you have to get things right with the different parts...
Save up some more, try to convince your wife of the extra costs (just say a Walmart bike will not cut it) and have a bit of patience.