When getting deals on Ebay or anywhere for that matter make sure the price includes everything. Some are priced pretty low, but don't include the antenna or transducer.

Lowrance products are water proof as far as having it in the open and getting rained on, but I wouldn't put it in a bucket of water over night. Probably the same for the other products too.

If you decide on Lowrance shoot me a PM and I can help you out as far as suggesting a unit that will meet your needs.