For commercial concrete cleaning you need a repeatable system of doing the job so you or you and your guys do it the same way each time so they are not fumbling around wondering what to do wasting time and eating into profits.
You need larger gpm machines and surface cleaners but the surface cleaners are sized to your pressure washers by the rule of thumb of 4" of deck per 1 gallon per minute of pressure washer pump output. You don't just buy a huge surface cleaner and hope for the best. That is not how it works and the guys that don't follow advice are soon selling their huge surface cleaners since they will not work with their systems.
You need good chemicals that help on the job, some jobs need recovery, some do not.
We cannot teach you everything here in a couple of paragraphs, you will need to go out there and learn the craft, become more efficient and price accordingly to what makes you a good profit, nobody knows your overhead and expenses so your profit will be different from everyone else's profit so asking what is the going rate is a question that is very hard to answer and not many if any will tell you what they charge as competition is watching all the time, your competition and mine as well whether you realize it or not.
You need to decide how much to charge so you pay your expenses and make a profit, nobody can do that for you. This should make good sense, if not then you should take some business classes and learn about business to help yourself understand the fundamentals of business.
I haven't been on this site in years. This was always the best forum for information. I learned alot here. 