Hello,
For creating a new fields in VehicleManager component
ordasoft.com/Vehicle-Manager-Software-Joomla.html
You can use Extra Fields manager and it help create new fields (VehicleManager :: Settings - Vehicle Page Settings - Extra Fields manager).
Put Show Custom Text Field - yes and you will get new textfield. Also you can rename your Custom Text Field in VehicleManager :: Language Manager (put Custom Text Field in Value constant and rename)
And for put it below the pricefield, you need knowledge of CSS and HTML.
Or you can write to our project form and we will try to help you.
ordasoft.com/About-us/OrdaSoft.html
Thanks,
OrdaSoft team.