You can reuses many of the 5L mini kegs. However, I believe the newer Heiniken mini kegs are not reuseable. I believe they have some sort of patented co2 charger which is not reusable. All the other mini kegs work on gravity dispense. They have a spout at the bottom and a pressure relief bung at the top. You can buy them new for about $10-12 a piece from homebrew shops, though they are becoming less available. The down side of these are they are not made to be force carbonated and you need to rig up a method of dispense for long term useage. Meaning they are intended to be emptied in a short amount of time since the allow air in when dispensing, so you will need a dispense method that tops up with co2 rather than air.
You can get corney kegs that are 2.5 or 3 gallons. They are not very plentiful and so, not very cheap when you actually find them. The ones I have seen were three times the cost of a used 5 gallon corney.
There are other systems out there too like the tap a draft which uses PET bottles and CO2 chargers. Or the party pig which is another PET bottle system.
You could always go to bottling...