Inverness, Scotland is on sale from many airports with Oneworld and SkyTeam airlines. American and British Airways both have discount ticket prices around $465 to $550 from San Francisco, San Jose and Denver and likely other airports across the USA. Delta/KLM is the lower fare in some markets, like LAX.
Lowest fares are travel in May and September into fall months.
British Airways AARP discount offers up to $65 off Economy class tickets.
British Airways AARP discount ticket
San Jose SJC – Dallas DFW – London LHR – Inverness INV – LHR – LAX – SJC
$466.77 round trip Sat May 5 – Sun May 13
British Airways AARP discount ticket
Denver DEN – Chicago ORD – London LHR – Inverness INV – Manchester MAN – Philadelphia PHL – DEN