Basically you want to build a 600m piece of road. I'd call your local earthmoving guy. But the issues to consider are:
a) What slope constraints do you want (ie how much dirt do you want to move). If you want it to be within 1% then you might be astonished about how much dirt needs to be moved.
b) What size aircraft do you want to land (ie how think should the crushed rock base be. 300mm is probably typical, but landing a C150 on a padock could get away with a few inches)
c) how weatherproof do you want it, ie how good should the drainage be. This might be one of the higher cost items.
Do you really want gravel? Why not just consider grading a flat surface on grass and making some drainage?