Replacing an oddly sized French Patio Door
A pair of 32" doors should fit easily. Any slop at the siding can be trimmed out with a piece that covers the existing siding. 

Go to a real door place. They'll be able to give you a reasonable price for what you want/need. And if you need a deeper jamb for the aforementioned overlap strategy, they're equipped to deal with that. I've hated every big box store door I've had to touch over the last 5 years.

I'm a little surprised that your contractor didn't tell you all this. (Well, except for the rant about big box stores... that might just be me.)

ps, if you must search online, use "64x80" for a size.