Argos have the LEGO DUPLO My First Farm for £19.99. It's also on a Free Delivery offer, so saving you a few quid there. There's another offer at the moment too, with 2 for 1 entry to Legoland Windsor resort with every Lego purchase collected in store, excluding mini figures. The offer for that ends 17 January 2014. It's also availalble online from various sellers I've never heard of, but this is still the best price.
Encourage creative play and animal recognition with this fun farm set. It includes a farmer DUPLO figure, a tractor and 4 animals. It also features a farm, tractor, pitchfork and assorted DUPLO bricks. So quite a few bits for the first farm.
The set is suitable for children over one, and obviously compatible with other sets.