For the type of access you have, I wouldn't bother with a bituminous surface, unless you're prepared to spend a lot of money. What is already there sounds basically OK, and I'd go with Bobert's suggestion of simply regrading.

Alternatively, Richard suggested adding some scalpings, which would make the regrading easier. Suitable scalpings are not available in all parts of the country. The more reliable option is Type 1 sub-base material.

Assuming an area of about 600 sq metres, you should be able to get a 50mm layer of sub-base laid for about £1200. Add a few hundred for initial regrading and levelling.

For more than you ever want know about paving, try McCormack's paving expert site. The relevant page is here - click on Price Guide in the LH box for cost estimates.

Phil