How do I ever thank them

My mom called tonight to tell me, she talked with my dad and they want to give us the money. My dad said he would give me whatever it takes to get me this baby. I can't even begin to tell you how much this means to us. It is such a wonderful gift! I am worried that this might not work. This is a like gambling with their $5,000. I did explain this to them and they seemed to understand nothing is a sure thing. I have always hated asking my parents for money, and I really hate accepting it. But without we have to take out a loan, or this doesn't happen. I was also trying not to ask my parents for any money because if we decide to adopt I will need their help then. But as much as I feel wrong taking this money, I know this is our last chance at a biological child. How in the world do I ever thank them for this gift?