She has to apply to her bishop for marriage permit with not a Christian. She will get it, so it's not a problem. Only requirement is that you will have to sign that you have nothing against children becoming Catholics.
This is absolutely true, my Dad married a non Christian, this was all he had to do; it didn't take very long for permission to come through.
There is no guarantee that any children you have will become committed Catholics; there are six of us offspring and non of us had any belief in the religion.
So since one problem is solved, only 2nd left - money. Women are not cheap, so be a man and save enough money for this ceremony if she wants it. You could only try convincing her to keep it moderate, because traditional Polish weddings are unhealthy sumptuous.
Stick to your guns about a small wedding! Explain that the money for a large wedding could be much better used on a deposit for a house. There are many other uses for it if you already have a house.
Also about the money, you should expect to get back at least 50% of costs from guests, so it's not so burdensome for your budget as may seem.
People are very generous but with the current economic situation it's better to play safe.
My brothers and sisters (and myself) had very small weddings but they were all beautiful.