I don't know if it was just DHL being arseholes. They had taxed me in the past even up to £50 when I had declared a $20 value, but it was also very round figures (£18, £36, £50), so I think they just plucked them from thin air. DHL is currently not an available option, although I would've gone with FedEx anyway as they are marginally cheaper. I declared $66 value, so fully expecting to be taxed, but it's a big package, so didn't want to risk putting down a very low value. Hopefully they'll accept it.