The idea of such an event is fascinating and I enjoyed reading about it. Although one comment on the site points to a difference between American and British culture: they say they set the story in the 1950s because it is "a 'vanished decade' in pop culture". Which is odd because in the US it is perhaps the most cliched decade thanks to things like "Happy Days", "Grease", faux-1950s diners like Johnny Rocket's, etc.
INHO 250 GBP is a steal for this kind of experience. There are more expensive shows where you sit on your ass as part of the audience and just watch other people perform.
In that case it's a typo, and should be spelled "God Rest Þe Merry", with a latin^Wenglish capital letter thorn, rather than a Y, which was used as a substitute when using early german printing type that didn't include the thorn character.
Unless you're actively trying to write in Ye Olde Butcherede Englishe, in which case go ahead.