Keep an eye out on kijiji this spring and summer there should be some good deals out there.
I don't know what your expectations are for a boat but I would suggest nothing smaller than a 14' and a 9.9 for you and the boy. I have now and have had a couple 12' over the year and yes they work but not the safest tub in the world. For something decent and in good shape you are looking at around 5 - 6g's with trailer you can usually find them quite nicely rigged for this price. New a 14' with 15hp, trailer and gear will put you up around the 8 - 10 mark depending on what style one chooses. Don't go cheap by that I mean the cheapest price/manufacturer they are cheap for a reason. For me there is only one boat and that is Lund but there are other decent boats out there. Like Chrestliner, Smokercraft, Princecraft and a couple others. But I will tell you this and this is no exaggeration, you buy a Lund it will last you a lifetime and more.