You called.
1) It doesn't rain all the time. The last 2 weeks have been SUN SUN SUN
For Example here is a pic I took last week (South East Scotland).
2) Like Lena says probably equivalent to the rest of the UK. Meals £15 - £20, accomodation depends on area and type but probably £40 -£100 per night (58-150 Euro).
3) Midges can be annoying so wear bug repellant especially up north.
Have a search of
http://www.visitscotland.com/ to give you an idea of what you are after.
Watch if you are planning on Edinburgh in August as the Festival is on and accomodation prices tend to rise.