The exchange rate is usually slightly lower than Bali in Senggigi, it is MUCH lower than Bali and mainland Lombok if you are on the Gilis. There are a number of money changers in the main street of Senggigi and a few in Kuta Lombok. Lombok is nothing like Bali in terms of 1. being ripped off by money changers - in my experience they are all safe to use in Senggigi, and 2. the sheer number of tourists, shops and money changers.
PT Central Kuta money changers, which operate out of Kodak shops in Bali, don't have any branches on Lombok.
My favorite money changer is at the southern end of the Senggigi strip, just at the bottom of the hill. It is a wartel that has phones and changes money - that's all they do. His rates are good and notes new and clean. He will also negotiate for larger sums being changed (e.g. a few hundred).