Why not try the numerous Travelodge's or Premier Inn's in close proximity to Inverness - they are often a lot cheaper.
Can't speak for Travelodge, but in high summer the various Premier Inn's around Inverness are well past £100 per night.
Last summer we found the Airport Marriott at around 60% of the Premier Inn best price - ok if, like us, you are travelling by car, or once the Airport station is open.
On another sleeper subject, whilst browsing in the 1966 LM Region train marshalling book I was interested to note the Euston to Liverpool and Manchester overnights conveyed four and five sleeping cars respectively in addition to seated coaches, very much changed days when I was using them in the 1980s and it was one sleeping car to each.