1) stay away from the Olympus tough series imho. Slow and inaccurate focus, so-so picture quality.
2) I routinely take my Panasonic TS3, rated to 12m, to 15m, for 75+ minute dives. So far it's just dandy. I have had the problem where I have not been able to do anything but turn it on and off a couple of times (oddly both times at 14.7m, but it's also worked fine at 15m LOL). Going up a couple of meters allows it to resume normal function. I adore this camera and recommend it IF you are diving in the recommended depths.
re the flooding on the TS series - the only flooding I have personally witnessed or heard of from first hand source that wasn't due to not locking the door properly or having crud on the seal was with the
TS2, NOT the 3, on a relatively short (45 min) 10m dive. From what I can tell, the TS3 is a huge step up in reliability in-water. Don't know much about the TS4 except that I personally wouldn't pay the premium over the TS3
Adding a housing is only a couple hundred more and that will allow you to take it to 40m.
Another inexpensive option is to check out the Canon SD series (fabulous little cameras!) and add a Canon housing. Canon housings are around $170ish and some of these cameras can be found for about $130ish.