If you price new factory brackets, you will find they are about the same price as the aftermarket variety. In addition if the stock brackets won't work for your application, you have to modify them. For a guy doing his own car, that's fine, but for those having the car built by someone else, the aftermarket brackets are much cheaper that paying for one off parts.

Some of the junkyard stuff is getting hard to find, particularly for the short waterpump versions, particularly big blocks, they only used them a few years.

I just did a new alternator bracket for a 500 Caddy in a 47 chevy pickup, the owner had to pay for four hours labor plus powder coating. If there had been a bracket available that would do the job, even $100 for that bracket would have been cheaper.