Yes it can be left on without disconnecting the battery. From memory it was about £100.
It's the second CTEK charger I have had and with all things you get what you pay for.
I use it for car and leisure batteries it has recovered a couple of batteries that were dead.
In my opinion it's worth the money. My LS 430 doesn't get much use but it's allways ready to go as the CTEK keeps it topped up.