I would advise yo uto not get a dog off craigslist. Not that ecconomic concerns are most important, but think carefully about the health of any companion. Do you know what health issues exist in the parents, their parents, etc? Take a very close look at the lineage for problems, you may end up paying for them over and over for many, many years to come...or perhaps worse, only a few years.
Make a list of the various dog breeds you like, I recommend looking at the AKC site (doesn't matter if you're in the US, they're breed generalities) and compare the expected exercise and other aspects with what you want. Having had both long haired and short haired dogs, I am unlikely to ever have another long hair due to the shedding. Some breeds socialize better than others, some are stubborn, etc.
There are a lot of dog breeds, so
here's a list that shows typical weight ranges to help you sort and find possible good candidates to later lookup and see how they match your lifestyle and expectations.
Also, here is a thread for advice to first-time dog caretakers, "
So now you have a dog..."