Depends on your definition of cheap and if your car is a show piece or not. Summit Racings sells hoops of 'em and they are rather inexpensive. Proportion Valves - Brake Systems - SummitRacing.com
Now, it all depends why you'd like a booster. Most seem to think manual brakes are the way to go and you lose 'feel' with a booster. If you convert to 2/4 wheel disc, then you'd have to change the master cylinder/lines/valve for sure and to be honest, it's an easy job. If you have the single 'jar-type' master cylinder, i'd dump in anyway for safety's sake. There are countles how to articles on the web converting to disc brakes. Look at JamesW's Home Page for starters. I have his site bookmarked. :bigthumbsup
Now, it all depends why you'd like a booster. Most seem to think manual brakes are the way to go and you lose 'feel' with a booster. If you convert to 2/4 wheel disc, then you'd have to change the master cylinder/lines/valve for sure and to be honest, it's an easy job. If you have the single 'jar-type' master cylinder, i'd dump in anyway for safety's sake. There are countles how to articles on the web converting to disc brakes. Look at JamesW's Home Page for starters. I have his site bookmarked. :bigthumbsup
