If you are talking about crossing two breeds and hoping there is a market for them that is a less certain way of making money. The dog that would result from the mix would be much like a pitbull limiting the market for them and leaving your son wide open for lawsuits if his breeding dogs got loose and did any damage of any sort.
In addition without training this sort of dog would be hard for him to handle too.
I know of no breed if properly cared for that can be raised with 'little' in the way of complications or in a way to make much of a profit. If however you son just plans to raised the dogs outdoors in USDA approved housing and with minimal care, no training, low grade food, and do all vet work himself he would be better off to look at the dogs that are currently popular with a wide range of people and are innately easy to handle. The labradoodle craze seems to be blowing over and the puggle seems to be of interest to people this year. Purebreds such as labs and goldens seem to have a steady track record in popularity as do small poodle mixes.
This site talks about whelping costs
This site has a lot of good links to read on the work going into whelping and raising a litter
Depending on where he lives and how he plans to market his pups he may need a USDA and/or State License so he needs to be familiar with the local laws and requirements for dog housing.
He also has to plan on staff to care for the animals if at any time he cannot.
My feeling is if you really want to make money in animals the best bet may be to start a pet supply store that sells the designer animal feeds and goods to care for pets.
In all the years I've raised pups the best I've done most years is break even but I don't stint on vet care for my animals or on food costs etc.
Hope this helps you!