If this were mine, I'd probably go for option #3 and try to negotiate a better price. Unless you are already getting the parts at, or near cost. It's easy to spend someone else's money.
You're looking at a $500 delta between brand new and best case iffy option. I'd want a firm quote/opinion from the machinist about either of the other crank options.
What's the history on the eBay crank? And does it come with specs from the machinist?
I guess it all depends on what your plan is for the X5; are you planning to sell it, or keep it?