After reading the article Upgrading Dropbox to 16gb for 25usd by Alain M. Lafon I realized that I had $100 in adwords credit that I had gotten for free from Google (by snail mail oddly enough). Alain had cleverly used adwords in combination with his dropbox referal link to get the referral bonus on dropbox. If you verify your edu email you will get double referral bonus (so 16 gigs instead of 8). If took me about a day to get all the referrals I needed.
UPDATED: Since posting this Dropbox has updated so that everyone get double referal bonus, so no edu email is needed.