I hope he has a large wallet as the price of Mahogany has gone through the roof over the last 10 years or so if you can get some.
I always price the job in Sapele as well now which is a reasonable substitute and the timber cost is better if the client does not realise how much it will cost.
I would be tempted to give him samples of the timbers.
You will probably have to use Honduras if he wants to go down the Mahogany route as Brazilian is on the banned import list, so either it will be old stock or will have been brought into the UK illegally.
Tom