all Apple laptops have their processors permanently soldiered to the motherboard, so no, sorry. Just get an upgraded 15" if money is an issue, or a refurbished one. Sometimes you even get new laptops from Apples refurbished store, and if the computer you get isn't 'like new' then Apple will replace it for you with a brand new one
Other than that how about a student ADC discount which gets you 20% off any Apple purchase? Do you qualify for that?.