I love Brother machines and have more than one, from a $200 walmart to TOL dealer machine, all great. Advantage with a delaer is lessons, service. advantage with one from a big box store is the return policy if by chance you get a lemon or just don't like it. The same models are not sold by dealers that are in big box stores but they can be very similar. I once wrote to brother to ask if there was an internal difference on similar models sold in discount stores or sold by dealers, they replied that the insides were the same.
Another dealer advantage though is the opportunity to buy a lower cost machine that has been traded in for an upgraded model. On a used machine you would get more features for the same amount of money that a new machine would cost.
If it were me my first stop would be a dealer to check put the used machines, I've gotten great machines that way.