The Aqualifter is a water feed pump. Powerheads work too, but are usually overpowering and cost more. The lifter is about $15. You also need a co2 regulator. Yoiu can buy a co2 bottle for $75 or so, but usually gas shops just do tank changes, so you may want to check with them first and see what rental fees cost.
Optional is a pH controller to make the system automated.
You can get the JBJ reg /Milwakee controller combo on ebay for about $175, thats a great deal.