Out of interest and in your personal not professional opinion (if that matters), what is a likely range of costs for these services?
"Pension taper problems" is quite a vague problem, but I don't think it will be hideously complex depending on the specific years (e.g., rules around annual allowances have changed in the not too distant past and could complicate things) and how far back calculations need to go.
For an existing client probably less than £500+VAT, maybe half that assuming doing some early year or current year calcs and with historical data, for a one off client I wouldn't do for any less. You've got all your AML admin to do which takes time and won't be recovered in future years for a one-off job. I'd potentially even say no thanks as it's a potential can of worms with little to no thanks for the effort.
Also - people think they pay for the time to do something. They don't. They pay for the years of knowledge and experience we have.