Inverness is very convenient, and also very cheap to travel to with easyJet. I always fly to Inverness from Luton when I go to Scotland (mostly to the Isle of Skye). The drive to the coast is beautiful, especially the Lochcarron way.
There are several car hire firms at Inverness Airport. easyJet has a deal with Europcar. You can book a car cheaper when you have booked your flight with easyJet.