The worse case price of a rearm kit I have seen (includes gas bottle, activator and two types of clips) is £20 less any discounts. you usually have to replace these every two to three years, there is a date on the activator, usually not a date on the bottles, these can be weighed but we change them or save them as spares, likewise the old activator can be saved as a spare for temporary fix for a discharged life-jacket until a new kit is purchased.
Regards
Alan