Guinea pigs are species specific animals. In my opinion all animals should stay with there own species. Hamsters will attack the guinea pig and rabbits can potentioly kill it. Guinea pigs need their own kind.
Do not buy. Check out
Pet adoption: Want a dog or cat? Adopt a pet on Petfinder for adoptable guinea pigs in your area. Don't breed or buy while shelter animals die.
After all the numbers we've given you you say yet? Breeding guinea pigs EVER is a bad idea. All the money in the world sometimes can't save a lethal for sow having trouble giving birth.