I've dealt with a similar situation. Some people just don't consider money important until they don't have it. You won't be able to change his ways so don't try

I've dealt with a similar situation. Some people just don't consider money important until they don't have it. You won't be able to change his ways so don't try. It will just be unproductive confrontations. An agreed upon budget might help. The budget should have a line item for these type of items. But I suspect you already have a budget and he's not following it. You won't be able to change him so you need to look at the situation seriously and decide whether it's worth continuing. The reality is that startups without financial discipline will have a hard time surviving. Good luck.