I tried looking for another spa in Sanur, but I always ended up at Madurah Spa. The prices are definitely within your budget, so you can opt to take several treatments in one day.
I'm not surprised that you heard that Nusa Dua has the best spas in Bali. I'm sure that there are many great spas throughout Bali, but in Nusa Dua the big resorts have amazing spa facilities. The Bali Grand Hyatt has an amazing spa, which has also won some awards. So you can imagine how that looks. I've visited it and made pictures which can be seen on bali-travel-life.com/bali-hyatt-hotel.html.
But not surprisingly the prices are high. For a 75 min treatment expect to pay 100dollars. They usually have a whole list of special treatments that you can hardly find anywhwhere else. You will need to make reservations in advance though.
I agree also re Mandurah Spa, clean, friendly, good treatments, very well priced. Doesnt look flash from outside but highly recommended. Here is their link
sanur has many places to choose from. mandurah is popular but if you just want a cheap massage or treatment of some kind there are places all along the street with massages for as little as 50,000rp. AB in hardys has a very good massage for 50,000rp for one hour. as for nusa dua being better well it depends on what you are after. the prices at the 4 and 5 * hotels are very expensive. have just stayed at grand hyatt again and the treatments here are world class with prices to match. for $100 you will get a lot more at mandurah in sanur.
I'd also go with Mandurah spa - Just went there twice last week, and it's great - One and a half hour massage & treatment was 150,000RPH. An absolute bargain. Definately the cheapest in Sanur too, though I don't know why because it is such a nice place.
I had a 3 hr spa morning last week at Mandurah including massage, salt scrub, flower bath, facial & hair cream for I think $40. Definitely recommended but be warned, the Balinese have freakishly strong hands & fingers.
We just returned from a week at Bali Hyatt. We had a free 1 hour massage in the Spa at Bali Hyatt which was fantastic - and the price was right :)
The Spa at Bali Hyatt is very nice, small but with an intimate feel about it. Not cheap though, US$100 doesn't seem to go far there.
The beach side massage at Sanur is 30,000 ruppiah for half an hour, and it varies where you go - Pink Ladies is OK, but it's certainly not a spa experience.
we stayed at the bali tropic nusa dua last nov had a fantastic time,massages are cheap and leave you feeling fantastic my hubby and i had two each at the same place.
Sorry i cannot remember the name but it was outside the hotel turn right up the road then on your left . cost £9 each well worth it for just over an hour of head to toe massage
best spa in sanur is natural spa, at a corner of jl. danau tamblingan and abian srama at by pass ngurah rai, just ask taxi driver they will know,or come to sanur internet service, jl. danau tamblingan(next to circle k & piccadilly), their kindly staff will give direction to you