The real question is: what is it that you get for what you pay for. You need to compare apples with apples. Cheap can be very expensive especially when your visa application is on the line.
So really what is it that you get?
Scenario 1: a document drafted by someone who has years of experience in US business immigration and whose sole focus is to deal with USCIS all year around. The activity of that type of consulting firm really depends on the success of the visa applications of its clients. So the success rate is a big deal for them. Usually, their website revolves around their US immigration business plan expert.
Scenario 2: a document drafted by someone with no experience in US business immigration. In a nutshell, it is “a blind leading the blind” type of scenario. Overall, the end document is foreign to the constraints inherent to the visa application. This document can trigger a denial for that very reason.
Scenario 3: a document advertised and sold as an immigration business plan while in reality, it is just a business plan for a bank loan or investment purpose because this is what the business plan company really does. There is hardly or no tangible US business immigration expertise in the background and consideration given to the visa application and underlying issues. The focus of these companies is pretty much on selling the same product regardless of what it is for. While this option is already better than scenario 2, it is still a bit of the same type of scenario. Odds are there is no picture of a US immigration business plan expert on their site.