We use crushed road base in an equipment parking area that works well.
Consider drainage and your native soil too- we have sucky clay and we mix in (powdered) cement, then water and compact (roll the tractor back and forth… for a long time) then put the road base over the top. Our parking area drains to the back well enough to not puddle.
Relatively inexpensive for the area we need to keep drained and clean-ish, barn helpers can do the work and it lasts pretty well.
For boarder parking, we have compacted decomposed gravel (called different things in different areas) with some concrete added for stability, then bird’s eye gravel (kind of like giant sand particles, maybe pencil-eraser size, and rounded) over the top.
This combo is fine to drive on, and also OK for the horses to walk on whereas pea gravel is bigger, rolls, and the pieces are pointy enough to hurt the sole of a horse’s hoof. But the birds’ eye gravel would get mushed into the base too quickly by the very heavy equipment, so we used the larger, courser road base (basically, that is crushed up concrete chunks, bigger than pea gravel) under the heavier equipment.
Stuff like this- always a good idea to talk to the counter guys at your local building supply place (not Home Depot, but the places where contractors buy material) and you can usually learn useful things about the local conditions and customs, and what materials are used in your area for these kinds of purposes.