SR and RM ( who really until this link up are just a marketing company ) are both at the top end of expensive .. so combined it will be doubly expensive ...
I'd say definitely <20: in all probability <15, and none of the known ones in especially good grade.
Even virtual washers go for very high prices. For example this one went for £3,600 hammer at LCA in March 2018:-
That is what i’m referring to, this is the obvious reason they bought into sovereign rarities. Strangling the collector for even more money. SR are also expensive
My own 1877 F90 originally went up at 99p so I immediately contacted the vendor to tell him it was worth thousands and not to accept a tempting cash offer. Wound up driving up to Derby to inspect the coin before paying an arm and a leg for it !