Tom, do not forget the tax and Vat which the original purchase will take a knock.
Yes - but including VAT the average new fibre cylinder costs £150, including Guerrillas as described above. The difference on top will be postage if its ordered as opposed to bought from the shop or at an event.
http://www.lips-paintball.com/acatalog/NEW-Guerrilla-M4.5-Reg-68cu-Air-System.-3687.html#.UvFDQvtBo1I
http://www.lips-paintball.com/acatalog/Guerrilla_Air_48_cu_4500psi_Air_Systems.html
Also, bottles bought new from a supplier/shop will not have a full 5 years use before the first test. This will depend how long the item has been sat on the shelf. Years ago, i have bought bottles with only 2 years left before the first test.
Yes, you wouldn't get the full 5 years / 60 months out of a cylinder, but to charge full price for 2 year old stock is a bit naughty. I've also bought old cylinders from new, but at a discounted price. (Heavily discounted, but I even had the cheek to look at every bottle for the dates and there were two batches with about 6 months difference, so I took the newest)
My calculation is just a guide, and its standard asset depriciation but excluding residual value. (The full calculation should take into account scrap value, a secondhand value if planning to offload or any disposal costs).
Also the retest price will vary depending on the circumstances of how the individual gets their testing done.
Its right that secondhand cylinders tend to go at £80 - £90, but if this were a full sale thread it would have all the dates, then people can decide for themselves. You could in theory buy a cylinder for £80, use it for a year and if someones willing to buy it for the price then sell it on for £80 thus getting free use, or you could buy one for £80 and have it become worthless a year later (unless you sell the regulator)
I doubt we are going to agree, but just accept that 'worth' and 'what you might get someone to pay' can be two different things