Out of your wallet today, if you can hand it over and collect to a site or dive shop etc to arrange testing it could cost you about £25
You're only going to get 2/3rds of the value of that test though
The cheapest new bottle will be an aluminium 3000psi at about £30 lasting 5 or 10 years, a fibre wrapped 4500psi will set you back £150
You can go somewhere inbetween with a new fibre cylinder without a regulator and transfer your existing one (if you can unscrew it without damaging threads)