PLEASE HELP SAVE GATSBY'S LIFE!

Hi everyone, this is the child of my life Gatsby! I had moved away for school and needed a friend. I adopted him from a shelter where he was passed on by others due to much younger puppies that were available on site :/ From what I was told, he was given up on by two separate families. And it's not because he's a bad dog, it was just due to unfortunate  circumstances - even though I don't believe any reason is justifiable! It's like giving up on a family member, I just don't get it. I knew that when I saw him, he was the one. It was love at first site! All he wanted was a loving home, and he couldn't of expressed it anymore when I walked up to him. Gatsby melted my heart. To make a long story short, for the past month he's been unusually low in energy and was sleeping a whole ton. He would also whimper anytime I left his sight. I also noticed that he was (or at least I thought he was) gaining a lot of weight. Friday morning I was woken up with Gatsby crying and he would just not sleep. I took him in for an exam and they discovered a large mass in his abdomen. Given its size and density, they said it is a malignant tumor (which is cancerous). From what I was told, if it is not removed and left untreated, it will eventually metastasize.. meaning it enters the lymphatic system or the bloodstream and spreads to other parts of the body. I was able to cover the pre-op tests such as an x-ray, ultrasound and bloodwork.  But the remaining balance of the removal is estimated in the ball park of 2,300. My life is currently being swallowed by school and I don't have the best paying job.. I'm graciously asking for anyone who can help Gatsby, it would mean saving his life. I promise that you would be saving  one of the sweetest, most pure and loving soul in the world. This is extremely hard and confusing to deal with. I'm not quite sure who or where to turn to. Gatsby is fighting against time, and there isn't much of it. I'm just afraid of it worsening and spreading. I'm praying and hoping for a miracle that this will all be over soon. Thank you for anyone that has taken the time to read this.