5x7 cameras come and go on the bay and patients is what will be required of you.
I waited and waited for just the right camera to come along... and it did! I ended up with a restored Deardorff 5x7 / 4x5 camera with the reducing back. And, the pricing was quite reasonable too.
Then, they disappeared and I've only seen the odd one pop up on the block in the last year or so.
So, be patient... you'll come across just the right camera at just the right time.