It also depends massively on where you are in the country. Down south is going to be way more expensive than Scotland and by some considerable margin!
I read on here of a guy paying £7k per year for about 600 acres in Surrey with roe and muntjac, so thats almost £12 an acre and about the highest I've seen (though thats not to say there are other higher cost leases out there - I just havent heard of them). Equally some of the syndicates that come available in Scotland on here in the Stalking Opportunities section can be £4-600 a year for 3-4000 acres with red and roe. Rarer deer will also bump the price up - So once you start adding in sika or CWD you would also expect to pay a bit more. So dependent on location, acreage and species present anything from 12p an acre to £12+.
Also bear in mind that some leases will allow you to keep everything you shoot, others only some of what you shoot and some will not allow you to keep anything or is sorted out via agreement with the game keeper at the time.
There are also people who have stalking rights, keep everything they shoot and pay nothing more than the odd carcass here and there and a bottle of scotch at Christmas.
Ultimately only you can decide if the price and T&C's is acceptable and if you're prepared to pay it. Its true what the say though - the one thing they are not making any more of is land, and the price of it is only going to go up.