1p is common, but this really depends. Just to give you an example, let's assume I have to fly LHR-LIN and the flight I want to is the 7:40am flight on Aug 14, which costs £234. However, I can also book this flight as an RFS for 2,250 Avios plus £42.50 in taxes. So after subtracting the taxes, you're left with £191.5 which you can pay with 2,250 Avios, which means that in this case one Avios is worth 8.5p. Obviously, there are lots of other considerations - are there other carriers you're willing to fly on that route that are cheaper? Are you willing to fly to MXP instead or take a later flight? Or take an easyjet flight to Bergamo? This gets even more complicated with long-haul flights, where I would fly in J or F if booked with Avios, but WT or WT+ if I book the ticket with cash, so it's hard to quantify the difference, and also availability is limited.