I would strongly reccommend that you get the advise of an experienced land agent before tendering for something like this. His fee will be money well spent.
Smallholdings like this often get let for a disproportionatley high amount per acre, because of their "desirability".
It'll also depend on the length of the lease that's up for grabs, and how much of the property maintenance will be the tenants responsibility.
On the whole, agricultural land rental is pretty dear at the moment - I heard of a piece of grazing land anglesey let recently for £270 / acre / year, with no buildings or house. Croppable land would attract a higher rent. Pony paddocks go for a hell of a lot more.