Donna guest house in Sanur is a good choice. Stayed there for 3 nights only last month. I think we paid around 200,000 Rupiah a night (knocked her down from 300,000), which is about £15.
Comes with a decent breakfast as well ( Omelette, fresh fruit, pot of coffee/tea) which you should take into consideration, as most other places you will go to get breakfast from are going to charge you 40,000 per person.
The guest house is clean as well, which is a major factor. Unfortunately, Indonesia has some filthy places to stay, and hygiene doesn't always come at the top of their lists!
we stayed at Samas cottages in Ubud & had a nice stay. The bungalows are basic but clean, they had comfy firm mattresses, and a simple breakfast. I think we paid about 200,00 IDR. It is family owned with very friendly staff. It is out of the main drag fray so very quiet as well. The best part, however, was the pool.