Perhaps there are luxuries in our budgets we can do without. Through our creativity. Many of us could think of some ways to make extra money and give it to missions. A woman I know bakes wedding cakes to get her faith promise money. A pastor friend gives his honorariums from outside speaking.
Businessmen sometimes commit a facet of their work to missions, and give all of that income.
Some take on extra consulting, or make the yield from a certain investment available to God. Children might sell lemonade on the corner, do extra yard work, or give some of their birthday money to missions. There's more money available for missions than what we presently can see. Through unexpected income. God sometimes passes an extra blessing on to us, money totally unexpected.