What's a fair price for....

Just like bleeding your brakes. Drain the fluid from the master cylinder and fill with fresh. Open a valve and pump till fresh fluid comes though. Repeat with the other wheels till finished. That's how I did my 65.
A friend opened the brake line at the master cylinder and all of the valves. He used compressed air and blew the lines out. I did that with fuel lines. He used low air pressure and secured a plastic bag to each brake line. Blowing gently he cleaned his lines quickly