Those rates sound high to me. I would check directly with your auto associations for the rates, based on the actual countries you will be visiting. Their website may not be up to date. For example, India has dropped its duty rate significantly in the last year.
I would also check with the UK AA, since you are planning to buy the bike in England. You can't reach the carnet department via their website, but you can reach them at +44-1256-493753 or by E-Mail to firstname.lastname@example.org
They can fax the application forms to you, but will require originals to be mailed back to them before issuing the carnet, so allow time for that.
Good luck and safe travels!
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