I've been around in Penzance for long enough to remember the shysters and sharks who tried to make a fortune out of the Total Eclipse centred on West Cornwall in 1999. It didn't go well for most of them long term, and I speak as someone very much involved in running a business legitimately in the area for thirty years. You may rest assured the vast majority of Premier Inn staff will not be profiting from this greed, and the old excuse of 'market forces' will not wash. The local area (Penzance East ward on Cornwall Council) is one of the most deprived in England in official government statistics.
Looking on Booking.com it's on the high side of the price range for hotel/B&B accommodation in the area during that week, but by no means an outlier. All these business need to survive somehow after a pretty disastrous and are going to charge whatever they think the market can bear.
They're clearly banking on a bumper early autumn, so that's good news for the buses as well.
I've just been looking further at the timetables and maps on Traveline.
As previously mooted the LEC (Land's End Coaster) is diverted via PZ Promenade to serve the Jubilee Pool. The stopping arrangements at the pool should be interesting! Not sure what I think about it missing out the town centre given its role as an important local bus service as well as a seasonal tourist service.
On the 17 alternate journeys are diverted via St Teresa's Care Home near Long Rock. Excellent idea especially as the section of route between Long Rock and the by-pass is a stop-less no man's land.