No idea about the second.
On your first point, auditing is an essential function of pretty much any organisation operating in aviation nowadays. If an organisation has a quality manual / exposition / handbook (same thing!) which requires internal auditing, then it'll also state who may conduct, record, and sign-off those audits.
The normal mechanism for gaining approval for somebody to fulfil this function (or any other that involves signing for things) is to send the CAA a form AD458 "biographical details of senior staff", which is then signed off by the CAA's appointed company surveyor.
CAA often resist (for both good reasons and bad ones) any "minimum qualification creep" in AD458 approvals. Instead, they look at the overall biography of an individual, usually send somebody over to interview them or watch them at work, then (assuming all is okay) sign them off in the role, possibly with a few caveats.
So, if you are looking taking on the role of internal auditor (or a specialist in other roles) for a company, the thing to do is get them to submit an AD458 for you as-is. When they come to interview you, discuss whether they see any gaps in your knowledge that need to be plugged. If they do, then what they should do is issue a conditional approval "authorised, subject to completion of **** course, and #### training, within ^^^^ timescale / before starting work in this role". This is a pretty time-honoured practice and I've heard nothing in recent years to suggest that CAA were planning to change that.
As to specific courses, well there are several ways of looking at this. £2000 for 5 days is a little high for this sort of specialist training, but not particularly out of court. Most of us want to improve ourselves, and progress our careers for bigger and better things - which is the sort of reason that these courses exist. In most cases, companies send permanent employees on them as part of a staff development plan - if you are a contractor then you can always try this with the main company you're working for, but frankly it's the sort of reason that as a contractor you are paid so much more than most permanent staff - you are expected to maintain your own professional skills and everybody recognises that this takes time and money.
Incidentally, if you are looking at such things,
http://www.cpda.org.uk/ is worth a gander.
G