Summer Tubbin':
The poor mans pond, or at least a great way to find out if a pond is for you BEFORE making a huge investment!

Day 1, brought home cheaply tub from Walmart, later determined that a round shape would have worked better in preventing bowing of the tub from the water pressure.
Cost: About 6 dollars
Day 3, bow is really evident, placed two cinder blocks along the side I outlined in red, and the railings of the deck took care of the other side. Worked great.
Added three small sections of water hyacinth.

Added 5 White Cloud Mountain Minnows from one of my indoor tanks to this tub.

Cost: 4 dollars for plants
Total Cost: 10 dollars
Added some liquid aquarium plant fertilizer I had laying around for my indoor tanks on day 1, remarkable growth in under a week, I see why it is illegal in some states to have this plant due to the way it can grow and take over a body of water in a very short time.
About 2 weeks into the project, the stagnant water really turned thick with algae, you can just make out the cinder block along the center of the right hand side of this picture to help control the bowing.
By the end of the first month I was disappointed in not being able to see any fish, so I added a spare power head with some large air tubing from the shed. I bought a large plastic plant pot from a local flower shop and a large plant from my local Aquarium Society Auction for a dollar.
Designed mini-filter system.
Total Cost: 17 dollars
Well this was the final results. I didn't get any fish to breed successfully, I did get some eggs but that was before I added the makeshift filter system.
Relatively cheap, granted I was lucky to have fish and a spare pump handy, if I had to buy everything I figured the entire summers project would run well under 45 dollars. Not a bad price considering the enjoyment and compliments I got from the envious neighbors.

Nice thing now is that it is getting cold the fish go back indoors, the plants were discarded and everything else is conveniently stowed in the tub ready for next year!

Blue= Tub Lt. Blue= Water
Green= Planter Pot Dk. Green= Plant
Black= Power Head Orange= Roots
RED= Brick Purple= Water Flow

I just placed two bricks in the tub to lift the pot off the floor of the tub a few inches, this also had the bonus of providing the fish with a cave-like place to hide.  The pot was a standard garden variety one made of plastic and had the drain holes in the bottom. Once set on the bricks I made sure the water line was about 4/5 ths of the way up the outside of the pot. I then inserted a large plant into the pot, the roots made for an excellent pre-filter as they grew they became very dense. In the center of the roots I placed the power head, for added protection to the powered I attached a bio-bag ( empty filter bag ) around the inlet and secured it with a rubber band. Then attaching a section of tubing to the outflow of the power head that would run up and over the top of the pot and 3/4's down the length of the tub.

The system draws water up from the bottom of the tub, in through the bottom drain holes of the pot, through the roots of the plant(s). Now the water flows through the bio-bag getting rid of small particles, into and back out of the power head up along the tubing back into the tub. Very basic water flow method that doesn't cost a lot nor does it draw a lot of power, even the smallest of power heads would work.