A furnace to keep a family warm

I've never done this and don't really know how to begin so I'll just try and tell my story.
My name is Cheryl, I'm 61 years old. I've been married for close to 40 years to the hardest worker I've ever known although it hasn't been a high paying job. We care for our 21 year old daughter battling a rare life threatening condition and are raising our two grandsons age 8&10 to my eldest son. Money is tight. There's been no opportunity to save for emergency which were now facing. Days before Thanksgiving our fuel furnace broke down. Were told by a heating and plumbing company that the heat exchange box has multiple cracks and must be replaced. Were told the cost will be between 3, 500 and 6, 000. We live in cold Pennsylvania. I'm grateful the temps have been good but it won't last. I'm scared and I'm embarrassed to go public and ask for money, but I've exhausted all other options. For the sake of my grandsons and my daughter who mean more to me than my pride I'm here to ask for your monetary help and your Prayers. I Thank You from the bottom of my heart. God Bless You.