Having insurance and/or doing overnights would be different. And having two dogs instead of one is different to an extent. And even coming to your house a few times a day to check on them, feed, etc. requires a lot of dedication and I can see $30 a day.
I'm just coming from the standpoint of it being an 18(ish)-year-old with no insurance who can leave the house whenever. I actually would be extremely nervous to leave Ellie with somebody so young. I'd sooner she was crated at her vet's office and didn't have any fun b/c at least I'd know there were qualified techs and assistants watching her.
I used to watch pups for family and friends. In some cases it was worth $30+ and in others it was worth less than $15. Depends on the dog and what they require.