What rate do you charge when sitting for a dog and a cat?

Have the client enter the cat's information in Rover's system, then that system will bill accordingly, which is the cat is charged at the full rate. If they had more than one cat, then the others would be charged at the "additional" discounted cat rate.

Now, you do have the ability to modify any booking if you want to give the client a discount. But your rates are very low for house sitting, especially where you are located. I have to assume that your "nightly" rate of $30 doesn't cover a dog's care for 24 hours and that, perhaps, you charge for walks or drop-ins during the day and that you only stay overnight at the house during the evening hours. If that's the case, I would not provide any further discount. Look at what others in your area charge as an initial guide on pricing.