That's a smart way to do it. I used to put in ranges (basically contingency) of rate but I found myself consistently hitting a similar % of the higher estimate

That's a smart way to do it. I used to put in ranges (basically contingency) of rate but I found myself consistently hitting a similar % of the higher estimate and just started quoting the higher estimate with the expectation that I'm not a God and there may be unknown factors which could add in more cost. Usually people are happy as you say if there's trust and you show progress.