Janey has given you some great points to consider. There are a few small breeds that do well in small homes, but a puppy is TONS of work and even harder if you have never owned a dog before. There will be potty training and obedience training and socialization and teething and adolescent behaviors, etc, etc, etc, to get through.
You may want to go through a rescue group and find a young dog-1-2 years old who has already had some training. Much easier to start with, and much easier on your patience level.
If you go on the AKC website and look at the different breeds in the toy group, you can get a good indication of what breed would suit your lifestyle and then contact one of those rescue groups. The group could then match your lifestyle up with a dog that would fit well.
As far as adoption costs, they vary from group to group, but I personally would never pay more than $300 for a rescued animal, and less as the dogs age advances. In that fee you will get a fully vetted and altered dog, so you wouldn't have any costs for vet care until next years shots. The basic wellness annual vet visit is around $75 in my area, but that varies as well. You could call some vets around where you live and get prices from them.
Smaller breed dogs=less food and less treats, so based on the size of the dog, you can do your math there at the pet food store. Don't, however, go for the cheapest food, as the better quality foods are more economical. You feed less and the dog poops less as well.
And then there are toys...your dog will want to pick those out.
Whatever you decide to do, make sure you do all the research beforehand, so you don't get surpirsed after the fact.
dog rescue volunteer