So I assume your dogs live outside then all year round? If they don't, I would think about this again. Do you have enough space in your home to keep the rabbits and the dogs safely apart? Is there one safe room in the house where the rabbits can stretch their legs and run around without having to be restrained to a playpen? Even dwarf rabbits need a lot of space.
If you're going to keep them inside, a hutch is not necessary, so you'll be saving a bit of money there, but I think if you're between guinea pigs and rabbits, guinea pigs are definitely cheaper to buy and need slightly less space. Guinea pigs do need a lot of fresh vegetables though because they can't make their own vitamin C. My friend had a guinea pig that lived on its own in a large tank with nothing but shavings [yes I know, but this was 15 years ago and we were very young children] and lived to the ripe age of 8. I remember it being very entertaining and sweet.