House and pet sitting

Where do you live? country, region etc. Urban/suburban/rural? What is prt?

Find out what it would cost the owner to kennel the same dogs for 30 days and then charge at least 1.5 times as much as your base price. Increase the price if the owner wants you to pamper the dogs.

Good idea.

I think it depends on if you will be living in the house while they are away or having to travel back and forth from your home. Generally I pay top dollar to a professional pet sitter, but if were friend or family I would give them a smaller amount and then make up the difference by taking them out to dinner or some other such gift.

I would consider a reasonable amount per hour (estimate perhaps a half hour morning and night) and add a small amount for gas.

My pet sitter is a professional (she is bonded and licensed) in AZ. She is able to give them medications and other such needed care. She charges $18 for the first trip of the day and then $15 for the second. She spends a minimum of a half hour at the house. She makes notes daily about how the pets are faring. We also sign a contract which gives her the ability to take the pets to the vet if needed up to a designated dollar amount.

I'd suggest approaching it not by eye, but as a full-fledged project. A month is a significant amount of time, and it's easy to get screwed over by hidden costs.
To avoid guesswork, I usually use a basic planning algorithm that helps justify the price to both the client and myself.
Create a checklist of daily tasks. Once the owner sees the scope of work for 30 days in writing, a price 1.5–2 times higher than the nursery's will no longer seem excessive.