I can do this for you as custom work. It will be faster, without any pain for you.
Let me know if interested.
Ok, so how would I go about getting that field into the submit page? Can you give me some more guidance to be able to do this?
Yes, it is possible to add. You need to add a custom date field into submit page and after to show the date on vehicle page.
Is it possible to add an availability date field to the cars for cases when cars will be available to purchase after a certain date?