I recently purchased a great kit off ebay that had every piece of underwater photo gear I could ever need. Unfortunately, the housing was for a 1ds mk iii/iv (fits both) and I use a 5d mk ii. I decided to purchase it anyway so that I could keep the rest of the gear and resell the housing. There are a few minor signs of wear but overall it's in great shape. I know these housings originally went for $4,750 so I think $3,500 is a fair price. I am willing to negotiate though. I may even consider trades. For pictures, just send me a pm with your email address.
I also have an aquatica remote trigger that came with this kit. I have not decided whether or not I will keep it yet but it is still brand new, never used. If I can get $415 shipped for it, I will probably let it go.
Finally, my buyer flaked on my ds125 that I tried selling last month. I will do 325 shipped for it. Works perfectly. It is an older model but never failed me. Holds a charge well. Again, message me for pictures.