If you can stay just north of Senggigi, the best value is Santai Beach Inn, it is cheaper and more basic, but comfortable and friendly. I usually stay at Santai as I stay for several weeks and couldn't afford an expensive hotel
Of try the basic rooms at Windy cottages, or a bit further out Bulan Baru hotel.
Going the other direction, Batu Bolong cottages used to have some cheaper rooms.
Good luck finding anything reasonable in August though.