Oly and Canon have made their own cases for their point and shoot lines for years, as have some of the other brands on occasion, and once they're more than a couple years old, you can get them for very little. Tons of these have been sold. Set up a watched search on eBay for the broad category. That way you can shop to a price point on at least the case, which will be the harder part of the setup to find. Buy the name brand, no soft bags. Do check that the camera it fits isn't too old, it shouldn't be necessary to go back more than a few model years. RAW capability is a big plus, but harder to find. A case port that can take an add-on color-correcting filter is also a plus, IMO. Take the case diving with no camera in it to test it first, and learn how to prep the door seal.
Wait for one with little use, and even better if it comes with a tray, for ease of use. If the housing comes with a camera, fine, but the cameras are way easier to find.
You may be able to hit $60, $100 is probably easier to do.
As an example, I still on occasion use a Canon S70 in their housing. It's 7MP, does RAW, and the control layout and handiness is among the better I've tried. Those came to market 10 years ago, but take decent pics. I'll bet it would sell for under $100 if I put it up.
Craigslist would be a good place to look too, less buying competition.
