After checking out a few options, I settled on the HDX 9-Inch Twin Window Fan from Home Depot. (Unfortunately, it’s no longer available, but I’ve included a similar option below!) It met all of my requirements, and came in around $30. Both fans run independently of each other, so one can pull air out while the other pulls air in. At the highest setting it’s still only a mild hum, and the basic design isn’t too offensive. So we installed it in the window in our pantry/laundry room, which is right off the kitchen through an open doorway. (It’s basically an extension of the kitchen.)
You don't mention the size of the bathroom in question which will factor in on the sizing of the fan required. You may or may not need a larger capacity fan.
Since you are getting your roof done, try and catch a sale on a top notch roof vent for the exhaust fan. If you let the roofers install the cheapest unit available, you might be troubled by hearing the vent flapper bang on windy days or have a lot of cold air spill in from the fan ducting.
If you really need a higher cfm fan, match the ducting accordingly, seal and insulate it. Also seal around the fan cavity. Both are good ideas in the interests of heat loss prevention, air infiltration issues in both summer and winter, and general air quality control.
Be aware that high cfm exhaust fans can possibly cause issues with proper ventilation for gas appliances, particularly in newer, more airtight building envelopes.
Money buys quiet. The Nutone fans are noisy and not very efficient at moving air, if you had one out of the ceiling and in your hands you would be reminded of the old joke about the elephant coming across a naked man and asking him "how do you breath through that thing?". I installed an attic mounted fan that is essentially silent, only the ductwork interfaces the bathroom, the motor is mounted in the attic on isolation mounts. You can't hear it.
Kudos to all promoting matching the ductwork to the capacity. Solid ducts are best, flex ducting, while convenient, reduces cfm capacity more in any given length.
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