I do find it hard to believe that Derby's stadium is worth £80m - it looks the same as ours. Ours cost around £22m to build including land, so there's would be similar cost to construct. (although the land prices will be different)
Price of commercial land in Derby will be higher, but its not a particular expensive place and the stadium is away from the Centre of the City. As a rough guide residential property is at average National prices - £218,000.
If there stadium in worth £80m how much is the whole club valued at £150m? I 've never heard of a Championship club worth £100m or more. Aston Villa was bought for £76m in 2016.