Go to your local rubbish tip, get one for free. take the tap out of the top, wash it out with a bit of water, and start cutting. 1 rinse will expel the gas residue, 2 rinses will give you peace of mind.
Save yourself $30. You are not going to need a nice new painted one anyway. Generally look for one of the older 9kg bottles, lift them up as some are a fair bit thicker than others. The new ones are really thin, and only 8.5kg.