Re: trustees
I have the list and there are 61 pensioneer trustees on it.
Not all would be offering services to the public, as a small few would be providing their services to just one pension scheme (e.g. Cadbury Ireland Limited are pensioneer trustees, but I doubt if they would act as such for anyone else. But I guess there'd be no harm in asking them, on the grounds that if they refuse, they might send you some nice chocolate by way of compensation.)
To the best of my knowledge, there is no list compiled of charges of each of them, so it looks like your only option is to obtain the list for yourself and do the shopping around.
If you do, please post the results back here as it would be a useful exercise for others.