You are not going to find a price for the Britten on internet sites because it is infrequently encountered. The iron looks very nice with one "challenged" area around the nose. The fuse is a good one, but the missing sabot is a bummer, although typical of the type when fired. Replacing the sabot will be a very costly challenge and I'm not sure how it would look. A value is a pure guess, but it is several orders of magnitude dearer than the Parrott bolt.
If it is available for sale or trade, I might be interested in acquiring it. PM or eMail me if that is the case.
The 30pdr Parrott is also missing its sabot but as Carl noted with good iron. I'd say retail of $225 for it. We have one on the main site for $295 that has its sabot, but not much interest has been shown in it to date. It is also from the Mobile area where a lot of these were fired from US Navy ships at the various Confederate fortifications.