DD had rats and we kept having health (tumor's) issues - several of our rats developed large ugly tumors and I got tired of paying the Vet $50 to put them to sleep.
We now have 2 guinea pigs - we have had them for several months and we love them. They are cuddly and very friendly. DD takes them out into the front yard and lets them play. We also block off a large area in the house and let them run around and have floor time. We have girls but have read that the boys are actually more docile. They are very social and you should have 2.
They are very temperature sensitive and heat can kill them quickly. They should be kept indoors in a climate that is between 65-75 degrees. They also are vulnerable to drafty areas so place their cages with care. Ours are in our family room. We can talk to them and they do talk back, plus they know all our footsteps and chirp and whistle when we come into the room.
Our cage is huge - 3' x 5.5' - we built it with grids according to the directions we found on
http://www.guineapigcages.com/ this site is awesome and has tons of information regarding care, feeding, grooming etc. in the forums.
Piggys are vulnerable to vitamin C deficiency and therefore need a good quality food, Timothy Hay and daily vegetation. We feed ours OxBow kibble, a good Timmy hay that I get from the feed store and romain or red leaf lettuce. We add asst. veggies for variety (bell peppers, cucumbers, parsley, cilantro, apples, oranges etc). They are not necessarily "cheap" to maintain.
Do not listen to the people at the pet stores 100% - the majority really do not know much. A little bit of reading and research will take you a long way.
Our cage has 2 litter trays with a good absorbent litter in it and the rest of the cage is polar fleece with a layer of towel underneath. I pull out the trays twice a week, vacuum the poop out daily with our shop vac and then take the fleece out and wash it every other week or so.
Good luck, I hope you decide to go down the piggy route, we love ours.