Guinea pigs are great. But, they're always looking for trouble.
Medium maintainance, they require fresh veggies. I just give them grass in the morning, which I steal from my neighbor who refuses to mow their lawn. Yes, I get weird looks, but my piggies are happy and it costs me nothing, except my dignity.
They get dried food for lunch and for dinner mixed veggies.
You gotta clean out their cage once a week or it starts giving off a distinct smell.
Other than food and cleaning their enclosure, there's nothing really except that you gotta have 2 of them minimum since they're social animals. Except mine are antisocial pricks who only come out when they hear or smell food.