Het DT
I don't thing we can really quantify it in those terms.
For me, personally, I ask myself if I really need it. Now, in your question, the answer will always be "no"

Also, having said that, I also still buy myself a little something every now and again.
For me, I try to live as much as possible in poverty of spirit, so I try to stay focused on God as much as possible.
I also try to think more in investment terms, so that it is not just a treat but a lasting object. But with smaller objects, it's difficult to view them as investments. I try to live furgally as much as possible, but there is a danger in denying yourself too many things, as that might breed resentment too...
I do not have an allocated amount for treats, I try to evaluate each situation as they come.
Just try to keep an open mind about the spending and don't let it interfere with your spiritual walk
Hope that made some sense
Peace in Christ!