Its a bit of a liberty charging that for an unlock - especially when the contract is finished. Vodefone and Tesco both do it for free.
I wouldn't have minded staying with Virgin, but after speaking to 2 sales people, neither could come up with a decent contract to replace the one that is ending - don't want to pay so much each month anymore.
I think in your case it would be ok to go to a local high street shop as your 2 year warranty will soon be up. However, for people who are considering getting it unlocked this way, some high street shops will use a hack to flash the software to unlock it rather than going the way we do by putting a code into the phone to unlock - if hacked, it would then invalidate your warranty.
Sorry to sound a little negative, it's just for people that are still well within their 2 year warranty for the handset.