Two reasons
Shetlands
https://club8090.co.uk/forum/viewtopic.php?f=10&t=71575
Western isles and Mull
https://club8090.co.uk/forum/viewtopic.php?f=10&t=53688
If you are sensible and don't need facilities - then wild camping is still quite possible. move on after a night and keep out of the way (away from the big spots) - otherwise the (remaining) small sites around the west coast are still simple and often basic - although there are exceptions.
If you decide to come up - give us a shout - we can give you details of loads of good spots - places to go, things to see. Would help to know if you are two adults or want to entertain kids too. Or PM me for details - we are in Inverness - if you come up - you can't really miss coming through.
And if you come before June - ignore all the talk of Midges. And if it's windy they can't hold on too well....
We live up here and are very rarely bothered by them - but then we don't go out in the wet west coast in July/August when they come out looking for holidaying English folk!
Weirdly - we are heading for the Netherlands in May/June for three weeks. Wife is half dutch and we honeymooned over there on a tandem up the coast and back down inland.....cracking holiday - now with the little ones - may take the tandem with the four year old on the back We have good memories of Texel and the excellent cycle tracks - and some great campsites.
The ferry is £450 for the 4 of us, cabin overnight and the van (Hull or Newcastle - similar price).
The Shetlands from Aberdeen costs the same and is about the same distance.
Compared with the short crossings down South - it is not surprising that it costs more - just look at the distance it covers!