How easy or difficult is it to purchase butter on the Grex?

I would assume this is your cool way of saying Grand Exchange?

 

 

 

I don't think it's very easy, although I haven't tried it myself. People seem to hoard their butter for their own potatoes.

 

 

 

Give it a try?

The Culinaromancer's chest has a nice supply of butter, cream and milk. There isn't much butter but you can buy up all the cream and milk and churn it into butter. If you have your house in Yanille, you can also try loading up on milk from your larder and churning it at the nearby butter churn east of Bert the sand delivery man's house.