Referencing a textbox value from a determined value to a textbox range

Hopefully attachment is in this thread.

The cells on 'details' worksheet are the rebar weight and rebar cost columns, that I need to reference and link. Needs to go into light load email template.

I basically want to type a tonnage in the yellow tonnage box, and for that to reference one of the three rebar boxes depending what range it falls in to.