Honestly, you don't want to go cheap on anything on this project. As far as humidifiers go, you get what you pay for like c_granger said. If you don't mind emptying a bucket of water about two to three times a day, you can get one without a hose, but if you don't empty it, it won't do it's job at all so the hose thing is very nice.
I guess before we could help much further, you are going to need the dimensions of the "pond" and it's filter worked out. Be as accurate as possible. Also, you are going to want to start drawing up plans to help visualize what you are going to be doing.