We usually see $10 to $50 depending upon property. Usually it is not refundable. The higher fees are generally one time fees, which are fine if you are staying a week, not so fine for a one nighter. we used to stay almost exclusively at Residence Inns, liked the separate bedroom and living room and they had good breakfasts, but they have gone to very high fees for the stay that just are too high for one night. Best Westerns used to be all pet friendly with low fees, but that is changing. Now you just have to shop around.
In my opinion, like most fees and restrictive policies, large pet fees are being driven by a few bad guests. And if you had a room torn apart by fido, you probably would either say no pets or collect enough money to make it worth your while too. And before someone chimes in with the inevitable "charge the bad guest" post, just remember that bad guest will respond to that charge with the equally inevitable "dispute the charges with the card company" response. Innkeepers are left with charging everyone so they can pay for the sins of the few.