Need Help - Trying to find a cheap waterproof 12v power supply

I'm looking for a reasonably priced waterproof/resistant 12v power supply and since many of you are techies on here I thought you might be able to help me find a source for one.

What I'm trying to do is setup a stereo system for my outdoor spa. I have found a very resonably priced marine stereo system with a wired waterproof remote and everything that I can mount up on the spa itself and have the main unit in a waterproof marine case underneath. However I haven't been able to find a reasonably priced 12v power supply to power it. I have access to both 120v and 240v under the hot tub, but perfer to use 120v as I have a gfi outlet right where the power supply would go. Most stereos seem to put out about 4x50watts, but I'm not sure what there actual input power rating is.

I was able to find this on ebay, but would prefer something a bit cheaper.

Spa power supply - ebay

Let me know if you have any suggestions.