Before you even approach the Hong Kong Department of transport for a private vehicle cross border permit, you will need the following to even get to that stage.
- A Mainland Chinese Drivers license attached to an address located in the region, married to the China number plate.
- Proof that you have a personal company investment of no less than $1 million US dollars, with ex amount of staff employed, to even satisfy the Guangdong Public Security Bureau's Mainland China - Hong Kong cross border permit issuance.
Unless you have a valid GDPSB permit, the HK dept of transport will not issue their cross border permit. You need that documentation first.
I have heard that it is possible to rent a plate and the permit from an existing dual permit holder for about $50,000hkd per year, but not exactly sure on the legalities on how they do it per se. I've also heard that you can buy these permits off people using their name for $360,000, if you don't meet the strict guidelines, but last time I checked this out was 3 years ago, so costs could be even higher than what they were then.