For cheap transport, you carn't go past looking at a used moped for sale, as these offer best choice when looking for a simple mode of transportation.
Mopeds are very wallet-friendly. Pre-owned ones go for $1000 apiece on average. Some may cost less, but beware of these because they might not be in the best condition and you would have to spend more money on repairs. You would have been better off buying a new one.

As for gas mileage, the common 50cc kind is the best choice with 80-100mpg. Its low top speed makes it use gas more efficiently. There are faster ones, but unless you are trying to get away from a mass murderer (or a bitter ex) in campus, then you won’t need anything faster. Besides, most states only allow up to 50cc mopeds to be street legal, so this is actually a plus.

For those worried about a single puff of moped exhaust triggering a second ice age, you’ll be happy to know that gas mopeds have 20% cleaner emissions than ordinary cars. Electric ones are also available in the market.
Even though you will mostly be using this in campus, safety precautions should still be observed. Mopeds are tiny little things and could hardly be seen at night so install reflectors or lights or anything that can make you visible. Wear helmets, too. Helmet hair is better than cracked skull.

A lot of sites have used moped for sale. Compare prices and research models to see which one suits you and your budget.

NEW WILDFIRE 150cc SPORT SCOOTER MOPED MOTORCYCLE NEW WILDFIRE 150cc SPORT SCOOTER MOPED MOTORCYCLE 28 Bids US $999.00 13h 18m
49CC GAS MOPED SCOOTER MOTORCYCLE under 50cc with TRUNK 49CC GAS MOPED SCOOTER MOTORCYCLE under 50cc with TRUNK Paypal 26 Bids US $355.00 2d 11h 48m
2008 Burgman 400 By Suzuki Scooter Moped Good Cond 2008 Burgman 400 By Suzuki Scooter Moped Good Cond 19 Bids US $2,125.00 5h 31m
KOMOTO NEW 2008 250cc SPORT STREET SCOOTER MOPED KOMOTO NEW 2008 250cc SPORT STREET SCOOTER MOPED 22 Bids US $600.06 1d 16h 33m
WILDFIRE NEW 2008 150cc TOURING STREET SCOOTER MOPED WILDFIRE NEW 2008 150cc TOURING STREET SCOOTER MOPED 21 Bids US $280.65 1d 17h 3m
49CC STREET LEGAL GAS MOPED SCOOTER under 50cc w TRUNK 49CC STREET LEGAL GAS MOPED SCOOTER under 50cc w TRUNK Paypal 25 Bids US $405.00 3d 10h 36m