We did quite a lot of low input wheat growing back in the 0 ty's. when wheat was £60 tonne. From experience would not go lower than 160 kg / N per Ha. Yield really dropped off at lower rates. Wheat/ Fallow rotation.
We paid £118/tonne for calcifert lime. WE use variable rate spreading and can do the job ourselves . It is more expensive but we can use our tramlines and do it when we want. Have applied up to 1tonne/Ha, in patches. Good product. Hope that helps !