We use a babysitter when I'm working.
I have found our sitters through the findababysitter website. You have to pay to join - it's actually quite expensive, especially since it's purely a listing and they don't do any vetting or anything like that, but we have found a few good babysitters that way so has worked out ok.

You could put signs ups. In the end it's all a bit hit and miss - you have to go with your gut feeling on meeting them. Maybe we've just been lucky, but our sitters have been pretty good.

We pay around $17/hr. for 9-4 we paid $120. At the moment we pay $140 for 9-5. She does clean up after him and a little bit of laundry if she gets the chance. Another sitter we had insisted on sweeping and doing the dishes while DS slept, for the same price.

I consider nap time paid break time. These days he's better, but he used to sleep for such short stretches that I figured our sitter had really earned the break, you know? That said, I don't think it's unreasonable to ask a sitter to do a few things around the house while your son is sleeping, it's just something to negotiate between you.

One option since your son is a bit older is getting someone in who has a young child of their own - they will usually charge less since they are also caring for another child.

Good luck!