How much for a letter?

When a client asks "how much for a letter" and I reply £180 plus VAT it always sounds ludicrous, even to me!

But in truth, it's never just a letter - I need to understand the case, make sure that the person who actually owes the money is the same as the person the client tells me owes the money (you wouldn't beleive how often it's someone else entirley) , remind the client they can charge interest and check out the invoice figure and the figure I'm being told to collect add up.

And that (along with money laundering compliance etc) takes about an hour - my hourly rate is £180 which is how a letter can cost £180 plus VAT