Far as I know, the Prizm (at least the 1999 models) all had the 1.8L four cylinder with either a 5 speed manual, 4 speed auto, or 3 speed auto. Quite a difference in EPA ratings between the 5spd and the 3spd, as well.
If that Prism is the one with the 3-speed automatic and no torque converter lockup, RUN AWAY! The camry will walk all over it for mileage.
Is there a visual clue as to if it has the 3 speed/no lock-up converter vs 4 speed/with lock up converter, or do you have to drive it to actually find out?