The Belmond British Pullman train is used for a variety of one-day tourist runs that might actually be viable as splurges for normal folks. The fare can be as low as £315 for a 4-hour spin through the countryside and afternoon tea; given how expensive afternoon tea in a luxe environment can be, that prices doesn't sound awful for such an experience. The all-day trip to Bath from £425 per person would probably be enticing to quite a few people, as would the Highclere Castle visit, priced from £468 but sold out for many months.
The eleven restored Art Deco carriages look beautiful in the photos and are currently running with reduced capacity. (Actually, with the new anti-coronavirus rules, such tourist-train service may be suspended at the moment.)
Corporate website: https://www.belmond.com/trains/europe/uk/belmond-british-pullman/