I built mine with a P32 and the batteries have lasted over three weeks and still have juice left. I've never left it out until they're dead. I just switch them out everytime I go to check which is usually every 2 or 3 weeks. The battery life normally depends on the amount of pics you get too. Also, in cold weather the amount of time they last seems to go down some but it is still good. As far as cost goes mine was around 230 for everything. Camera, housing, board, all the supplies to install everything, and the flash gasket. If you wanted to you get get it done for under 200. Watch ebay for good deals on the cameras.