Make sure you know what you're getting into before you get into it. It's a very time consuming and annoying task. My ex and I bred one litter of Pembroke Corgi pups, it was a litter of 8. I would never do it again.
Cost really depends on how you do it, and what breed it is. We got our girl an ultrasound so we knew how many puppies to expect. If you're not experienced this helps b/c if one is stuck it can be fatal to the mother and puppy. Tails docked, dew claws removed, shots, shots, and more shots. Shots usually aren't the most expensive part, but the rest can be expensive unless you do it a very inhumane way, IMO.
Make sure you have a lot of room and have a good system to clean everything. I really didn't find a decent system until the last couple weeks (We kept them in a round pin, zip tied a tarp to the bottom and filled it with horse bedding, so we could easily clean it out). One suggestion, get them pregnant in the winter or near the end of winter so you don't have to keep the pups in the house all the time.
We sold most of the pups for $600 each, while each cost probably $200-300 to take care of before we could sell them. Not much of a profit, unless you enjoy doing it. I definitely don't see myself doing it again.