Who makes, or sells the most cost efficient, bolt on power brake conversion for a 75 EB? I have everything as far as the axle, will need the booster, bracket, and cylinder...etc..

Check out BC Broncos, Uses a booster that is easy to find and fits great. It's a different design than the stock and works better for a conversion.
Also, Chuck has the best customer service.

http://www.bcbroncos.com/

Thanks man. I am getting a 75 soon, well in about a week. Looking forward to tweaking the hell out of it, and selling my ranger.