Gold Mobility rents a rollator for $99 a week. I've rented
ECVs from them and always been happy - their products are in good shape and meeting them for pickup and drop-off has been fine.
To me, a walker is the type with only two wheels on the front and none on the back so it doesn't really roll easily. I've had to use both for different reasons, and if I really needed a walker that was much harder to "scoot away", the rollator wouldn't work in the same situation. I sometimes call my rollator a walker so I know people use them interchangeably.
If you want a walker, not many places rent those so OMR is a good bet.