Well, there's a government PDF that gives the average price of land with planning in every part of England, it's a few years old now. The cost is per Hectare. There are 2.471054 acres to a hectare and 4,047 square metres to an acre. London is over £100m per Hectare, Cumbria is just over £700,000. Suffice to say, the average in Cumbria is £75 per sqm with planning. But you could have a crap area with a lower amount and posh areas with high amounts. So 0.25 x 4,047 x £75 = £75,881. But what's happening is, they sell at least double that.
There was a plot for a small house, 3 feet to each side of it, one car parking parallel to the house, tiny back garden asking price £45k. I offered £50k and was immediately told they had much higher bids. And I reckon I offered about £100+ per sqm. As for auctions, forget it. You need double the asking price, and then, you'll get outbid. It's at a point where buy a house, there's no return on it unless you live in it for a few decades.