I don't think I have a lot to add except this possibly...
Could you ask him what he might charge you to retrieve this one, fertilize it, see how it grows and bank it toward your next cycle? There is some tiny possibility there are two eggs there, which happens rarely, and if there are you could go ahead and if not bank this one for the next time?
The free cycle is so tempting. I'd also ask him how exactly he would change your protocol for the next one to get a different result. Is he open to other Dr.s protocols? Could your free cycle be an out of town cycle with Dr. Check running the protocol? (Or who ever you choose?) I know, crazy ideas but just tossing out possibilities.
I am so sorry you are going though this. It totally sucks. I have been there with the one follicle IVF and it stinks. For a while they thought there were two and DH and I were thrilled, but then they only saw one. (I can't remember what they thought the other was.) We were up against a wall so went though with it. (It was the last few weeks of our amazingly good insurance... I miss that insurance!
Totally personally, with the info you have given, I am not sure I'd go on since money is a huge issue to us, but as others have said, you need to do what your heart tells you. As I always advise, chose that you are going to do it for a few hours. How does that feel? Now, change your mind for a few hours and say you are not. How does that feel. One should feel "right". Also, about money... yes, it's a lot, I totally get that! But, if you are both working, how long would it talk you to make it back? Will it matter in a few years? Are there things you could cut back on to make it up, so to speak? It's about $7,000, right? Is it worth $7,000 to you to see this though? Will you be at peace if you don't? On the other hand 7,000 is a whole IVE at another place so that makes up for the "lost" free one. (Well, add in travel and monitoring and all that but you know what I mean!)
All the best to you, I am so sorry you have to be making this choice, I know from being there it is the worst!
Love to you,