I think anything more than 7 hull would be way too much. I get the point about old tech but even so, I don’t think the hull value is just representative of armour only, it’s also size & presumably quality of the space frame in general.
With that in mind (& other old tech - VSD, Arqs etc) is still say 6 hull at the most. And weak shields. Priced accordingly.
Lets also not forget, if in canon, these ships were relatively decent warships, it’s entirely possible the Empire tore out some of the guns, maybe even removed some of the armour etc to save costs or refit to the support role it now fills.