ok here goes for my first pond. To start with I used a 6' dia 350 gal cattle trough that I bought at the local farm supply store. I added two fluval fx5s after I had it up and running for a year, and also had to have it outdoor one winter and built an insulated box around it to conserve heat. I have all the plumbing through the side of the pond. Now I have added a 55 gal barrel full of biomedia. I run both of the fluval's outlets up to the top of the filter where it passes into some pvc pipe with holes drilled in every direction for maximum coverage. It trickles down through the media, and drains out into the pond. Bam instant cheapo pond. Fluvals were $200 a peice, barrrel costed $10, pipe, ect costed around $150, the trough costed me $160. So about $720 for the tank and equipment. The insulated box around it was about another $250 to build. Right under $1000 for everything and it works great.
My one was a simple fix for a big problem did some shopping about found a preformed pond then found a pond filter for sale in the local news paper ripped the guts out of the filter then filled it with bio media and had a sponge pr filter on the pump. Boxed it in to make it look nice.
Its in a very well insulated fish room I run 2 x 300 w heaters and it works fine. I have got a lid to stop fish jumping and this keeps the humidity down in the room.
Here are pics of mine again. I have koi and stingrays in it. I use a savio filter (looks like a large garbage can with a waterfall out the front) The waterfall on the corner also makes a nifty filter. It catches a lot of waste and is full of snails for cleanup. It is 12.6 x 15.6 feet. About 2400 gallons.