AS a birthday present to myself, i purchased a pond kit from Wal Mart for $83. It comes with a 600 gph pump and a 90 gallon preformed plastic tub, as well as assorted other details and plumbing. Personally i think its quite a bargain, not to have to deal with a liner and all that entails, and you can move it if you move. Its not even necessary to dig a hole for it, you can build up around it with stone or brick.
Personally I plan to sink mine in a hole where I removed an unwanted bush then build up to the rim of the tub with rock. While the kit comes with a stream spillway, I plan to build my own waterfall. Check it out if ya want a relatively cheap and easy water feature!