I don't have much interest in transfer fees but I imagine a top, top fullback at 25/26 would cost £25-30m so one who is 29 (by the time the season starts) would be £15-20m and probably at the lower end of the scale seeing as it's particularly rare for a top fullback to stay at the top of their game past 32/33 (as seen with Cole, Evra, Maicon etc. in recent times) due to the demanding nature of the role.