I was only ever a crew in that area so I have no idea about costs:-
The marinas in that area are Roker (Sunderland); St Peter's (under the High Level in Newcastle) - LONG way to the open sea; Braid (Amble) municipally owned but operated by C&N - LONG and possibly expensive hike up the A1 as every speedcam is loaded with film.
I don't know about Blyth, but it is well located.
If you have a bilge keeler prepare to get very muddy.
Enjoy your sailing there and send my love to Lindisfarne (Amble YC and Royal Northumberland YC (Blyth) have deep water moorings there).