Moisture Measurements Before Spray Foam Important Question?

What should I have for a moisture reading for the best results using open cell spay foam to the underside of the plywood and rafters using a moisture meter?
Also I'm getting quotes from sf contractors that seem to range from $.85 to $1.50. The amount of area is very large so cost it adds up when you have large sq. footages.
Can a spray foam mix be tweaked to cheat and that's how price goes down and up for quality?
And how about a contract? Some say they need no contract but what if it fails or begins to off gas a dead fish smell as talked about in another spray foam post to the point where it never goes away and has to be removed and replaced.

Moisture - most manufacturers have an allowable range, but the drier the better especially in hot roof situations. I am not sure your location, but for many areas Closed Cell is really the only way to go

Cheat the recipe - no or you will have issues (i.e. fish smell, not fully cured foam - foam with major voids). Questions to ask is will they be using a blower door to ensure they sealed up everything / how are they doing QA? Guaranteed thickness? For the lower cost ones, just whose product are you using / how long has it been sitting

Some places require a contract while others will say the quote is all that is needed - depending on the company I have gone both ways. Decent well established company with a great reputation, the quote will be fine.