Which scope is it that comes with it, how old is the rifle, how many pellets has been put through and has it been tampered with in any way?
If it's decent scope and both scope and rifle are in very good condition and it comes with all those accessories then you're looking at £600 being a good price....even £650 with the 4 mags.
Can't think why you'd need a spare air cylinder though as it's not the buddy bottle type