I can't help you with the cost, but yes appliances will need to be re-jetted for LPG. This usually isn't a problem, for example when buying a gas cooker you can specify that you want LPG jets for the more expensive things such as ranges, or get them as an accessory for off-the-shelf options. In terms of maintaining these appliances, just check that its burning clean and no debris accumulates near the ignition or burner holes.