I don't have any butter and don't have the money to buy some right now, but I really badly want to make a batch of cookies for some family friends who recently had a baby. Please help!
I can't have butter very often for various reasons and so most things I make I have to make a substitution. If you have coconut oil, that's fine though you may need to put it in the fridge before you use it, depending on how hard it is at room temperature. If all you have is oil just use 20% less of it and add that amount of liquid (water, milk...) as that's the approximate water content of butter. They will not be the same as butter cookies and they will brown faster have a somewhat different texture, but it will work.
Butter is about 80% fat and 20% water with dissolved milk solids. So replace it with a fat of your choice (preferably a more solid one like coconut oil, palm oil, lard, bacon fat, shortening) and water or milk in those proportions. A more liquid fat like vegetable oil should work too, but may change the texture more. You'll lose the butter flavor in any case.
I don't know about sugar cookies, but sunflower or olive oil make good subs in general cookies. I use vegan margarine due to my boyfriend's dairy intolerance and I've made some with oil to great effect. I measure by weight though so it kit be different if you measure by volume.