Firstly. This is a start and finish today job. If you arent available to do that. Dont apply.
I have a custom plugin, that offers a price for freight when Australia Post is unable to calculate a price.
The user clicks on a "freight quote" button.... admin then send the user a price for freight, which is automatically added to the users cart.
a. If a user has submitted a request for a "freight quote"
b. Admin had not yet entered the price in the wordpress admin for freight quotes.
c. If the user tries to access the checkout page, instead redirect them to the cart page.
Users with a freight quote pending, should not be able to access the checkout page
Changes must be done within the plugin, so I can upgrade other pages/plugins and it will still work.