It's criminally expensive in the UK. Here in Sicily you can usually find an Autogas station (for LPG fueled cars) that will refill a R907 bottle for under €5, and since marina electricity is metered, it's cheaper to cook with gas. A bottle lasts us around 3 months with two people living aboard and cooking 1-3 meals a day, plus espresso in the Bialetti Brikka of course
In Greece it was €15 for a proper Camping Gas bottle swap (and they even took the silly Butsir bottle we got in Spain), or you can find Autogas fillers in some places too.
We have an electric kettle which we use during winter season where we stay in marinas, and a Microwave, which makes great porridge quickly.
Recently I've found out that larger 5.7kg R909 bottles are available here too, but they do not fit our standard Bavaria bottle locker (both too wide and too tall).