The answer to that question is not quite that simple,
We sell several types of seed - short term 1 year medium term 2 - 3 year or long term 5 Years+, with or without clover? for hay or sileage? A traditional mix as per 1900's or a more modern blend? etc etc.
A Permanent Pasture mix will cost you around £72 per acre or less for 5+ Acres and is generally sown at 14Kg per acre.