You're going to pay $300 to upgrade that mac? Why don't you just save your pennies and buy a new one...you can buy a mac mini for $600 and just use it with your existing monitor, keyboard and mouse. I realize that's twice as much as the upgrade...but for $300 more, and a bit more time to save those pennies, you'd be so much further ahead.
I meant any existing monitor, keyboard and mouse...you obviously have at least the monitor and keyboard or mouse (likely both) or you wouldn't be posting