what does maccas pay? $14 an hour less tax? So you could offer $10 for 30 minutes cash? So long as it was walking distance from your place eg letter box drop your area. And given it would start out as a "hobby" the ATO wouldn't be interested in details.
I was thinking $5 per 30 minutes but there's no way I'd get out of bed for that. I pay the lawnmower man $30 for about 20 minutes effort on his part but it includes the mowers and fuel. And that's only once every three weeks, so you need to think about what people would be prepared to pay for daily, or every couple of days. Massage therapists are around $1 per minute but they usually have overheads. I get between $35 to $50 for 1.5 hours umpiring hockey but it usually includes an hour travel so more like $35 for 2.5 hours and I pay fuel etc. But I don't pay tax on that so it buys more.
you could also look up dog walking services in your phone book and ask them what they charge - rude I know but standard practice in business. And this would give you an idea of what you'd need to charge to make a profit especially if you had to travel to get to walk the dog (less than ideal).
Also be aware that if you say 30 minutes - it's likely to be longer really or you could be really mercenary and include owner chat time in the 30 minutes, or very politely remind the owner that the longer you chat the less time their dog gets walking.
You also need to decide - in conjunction with the owner - what kind of walking they expect, and what kind of treats work with that dog. Ie does the dog walk as fast as it can for the 30 minutes or is sniffing along ok.
Anyway it's not something I'm expert in, I know my neighbour hires one from time to time for when they're on holidays. They walk the dog, empty the letterbox (and stash it in a box round the back), and feed the dog when they get back - so the dog can stay home instead of going to boarding. The price for that is about the same as boarding. I noticed most recently it looked like Grandpa came round and walked their dog instead of the professional - might have something to do with what another neighbour told them about dog not getting a full length walk. Expect people to check that you do what you say and you treat the dog well (dog must be pleased to see you).