Prohibit $1000 vehicle with diamonds as payment method (4,4)

'payment method' is the definition.
(I know that bank card is a payment method)

'prohibit $1000 vehicle with diamonds' is the wordplay.
I cannot really understand how this works, but
'prohibit' could be 'ban' (banning is a kind of prohibiting) and 'ban' is present in the answer.
'vehicle' could be 'car' (car is a kind of vehicle) and 'car' is present in the answer.
'diamonds' could be 'd' (abbreviation for the card suit diamonds) and 'd' is present in the answer.
A single letter 'k' remains which might be clued in a way I don't see.
This explanation may well be incorrect...

'as' acts as a link.

Can you help me to learn more?