is it possible to create a custom transaction line field say displayed in the SO , this field copies the item rate when SO is saved. Then I want that value carried over and displayed to the related Dropship PO of the SO.

do this through SuiteScript, have the a script that updates the custom field and a script on the PO that will source the value and pass it to the field in the purchase order.

@Dean any idea how to do it,, like sample script