It would depend on the quality of the land, whether it has a water supply (for livestock) and adequate fencing, the size of the field and drainage (for tillage), access points and the part of the country you are in.
When buying the land, it should be sold with those details. Have a look in the local papers for where you are as there is ususally land for rent and that will give you an idea of the prices in the area you are looking. However, there is often a fair degree of negotiation that goes on!