For proper puppy care a puppy you must go to the vet and usually you will have 3 rounds of shots (1 every month) months and if you will spay/neuter then this will usually occur around 6 months or so of age for the puppy. Also you will have to get heart worm pills and probably de-worming treatment (also little pills) as most puppies do have some worms. You will have to bring in stool samples (puppy poop in a baggie) and have them test for worms and parasites, etc. for the first couple of visits. I believe I spent about 250 or so in total on all shots, de-worming and spaying. this will vary by state and by bet. Also Licensing fees are usually only $30 or so in most places.
If you don't think you can afford it, or aren't sure, then don't get a puppy. Dogs are a tremendous amount of time and work to properly train and will be expensive to feed decent food, buy toys for, buy a crate for, take to vet, etc. If you don't have several hours EVERY day to work with the puppy and give it attention, then don't get a dog. I walk my little lady every single day for at least 30-45 minutes, usually much longer.
Puppies mature to adults at different ages based on the breed. Usually around 12-16 months the dog will mature. However, it is very important to do research on your breed prior to and after getting a puppy to ensure you know everything about the dog.
I know this all sounds a little overdone for getting a dog, but it KILLS me to see people who aren't devoted and aren't prepared who have a dog that they do not care for properly. It is extremely important to work with the dog and learn about its health as a puppy in order to train the dog to act the way you want it to act, because when it gets older and bigger the dog can become an expensive nuisance (destroying furniture, clothing, health costs, etc.) if not properly trained and cared for. My puppy went from 10 lbs to 55-60 lbs in 5-6 months!
I have a 9 month old American Pit Bull terrier puppy named Chloe that I got about 7 months ago and I have done extensive research both before and after on Pit Bulls specifically as well as all dogs in general. I have had to be more careful because of the breed of my dog when it comes to training, however I do not think I would treat any other breed of dog differently as it is very nice to have a dog that is happy and respects and obeys the master.