Millings are not cheap but work great. Any asphalt plant will have it. They recycle it into new asphalt. Rent a skid steer. Take the grass down 3-4 inches. if you use rock you want whats called AB3 here. Limestone with every thing from limestone dust up to 3 inch rock. When it rains it sets up from the dust. Unless you use herbicide grass will grow up eventually through either. Driving on it keeps that down some. IMO your only other option is concrete or asphalt.

A cheap option here is RCA, recycled concrete aggregate, crushed concrete building debris from dust to 1 1/4" or so.... mats down good and makes a firm base. Used to be 15$ per yard, at one time there was so much available it was free for a 10 yard load....also makes a decent cement, just add the cement powder to the aggregate, no sand needed.

I used to have a limestone driveway. I just removed the grass and topsoil and put the limestone on top. After a while I added a little more limestone for settling. My maintenance was spray grass killer and level it about 2 to 3 times a year.

Thanks Brian. BB

Can't remember the name of it, but there's a chemical spray for limestone that will slightly dissolve the rock and kind of weld/glue the rock together so it wont wash or allow grass etc to grow thru it.