This weekend (29th and 30th), as part of the Big Finish Hallowe'en sale,
the B7 audio "Ghost Ship" has been reduced in price to £6 for the cd and £5 for the download.
However, it also appears that a lot of Big Finish B7 audios (including Ghost Ship) have recently become available on Spotify. If you use the free service, however, they are only available on computer. The paid service is needed to effectively access the audios on mobile. I'm assuming that this availability is not region restricted but I cannot say for sure. B7 audios also appear to be showing up on other similar services (e.g. Google Play).