It is currently £99 + £20 activation. They do have "promotions" from time to time offering free upgrades (last one ended in April I believe) so you could just wait and look out for one of those - but no guarantees of when of course. If you are a long term customer and out of contract you are due a loyal customer discount - so try calling 150 or 0345 454 1111 options 1-1-4-5 "thinking of leaving" (They are open Monday - Friday 8am - 8pm and on Saturday from 8am - 6pm. - 08.01 is best!) you usually get a UK call centre (it might still be a 30’+ wait though) Tell them you are thinking of leaving for Sky/BT because you can get 2 sky boxes for £x/month (find out what it really is before calling) and they will negotiate a new package deal for you with a second V6 and possibly reduce/waive new box charges. See what they can offer, if isn't good, call back next day at a different time and another agent could offer you a better deal.
-------------------- Services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.