The daily rental price varies depending on the location, demand and the condition of the units (either new or old).
For example, sewamotordibali.com rent the unit with price starting from 70,000 rupiahs (for customer using it infrequently) to 55,000 rupiahs (for customer using it frequently).
Other site, for example, www.sewamotor-bali.com offers cheaper ones. Starting from 65,000 rupiahs daily and 430,000 rupiahs weekly (7 days a week).
Any price in Indonesia is negotiable so I am pretty sure that 40,000 rupiahs per day for 2 week rental is possible.
Another solution, you can rent from any Balinese rather than from the rental agent. It might be cheaper. But be careful, the unit might no longer be convenient because of over-engineered customization.
Note:
Even though Bali is safer than other places in Indonesia, always double lock your bike and park at appropriate places.