I know this may sound bad, but look into some Vacation Bible Schools at local churches. It is usually $20-30 per week and you get to take them everyday for at least 3 hours. Not a bad deal. I wanted to limit how many my children go to, so I decided on two that offer their program during the morning hours. They have never been before, but I thought it would be a great way for me to have a little sanity this summer. I know for sure that they take four year olds, as that is how old my daughter is.
I am on Power and Southern and would also be willing to watch your son for a few hours, but obviously it would have to be in the afternoon if you didn't want to go the vacation bible school route. I have a fingerprint clearance card and I am CPR and first aid certified. I used to do daycare, but quit to go to school. Just let me know if you are interested.