Just a thought: buying a gun with money offered by your employer could possibly open up some trouble if, in the future, the gun is stolen and used for murder.
I could be wrong, but that's just the first thing that came to mind when reading your post.
I personally would go with the wheel set for the mountain bike, as you would probably get the most enjoyment (and exercise) out of it.
ALSO, nicer bikes are one of the things that I have found to retain resell value.