Okay,
Not going to get TOO drawn on my opinion on advice that includes “run around with a vacuum cleaner” except to say that evidence of deliberate clearing up is stated in guidance to be part of the reason to determine presence, not absence….
Look, if you want to understand what planning might require try this link: http://www.bats.org.uk/pages/batsurveyguide.html – its a free download and most, if not all, planning authorities and their advising ecologists will refer to it. This should tell you (especially from the development checklist) what to expect / what might be required and whether Phase 2 surveys might be on the cards, which will up the cost. It might be a bit full-on detail wise, but any quote from consultants should be in line with this guidance.
If you are after reputable firms for comparison, try http://www.cieem.net/members-directory but a word of caution – you may miss out on some perfectly good (more local) consultants if you just rely on it.
As a personal request, please try to do it right if you can at all afford to and pass up on the advice of the err – experts – above; some of us work hard at this stuff.
Cheers
Owen