The only reason I can think of for the price difference is that coinexchange.io has their wallet in maintenance mode, stopping deposits and withdraws untill they have updated. Whereas yobit seems to be continuing on the old chain at this moment. I have been speaking with coinsmarkets about their upgrade, and for a short timt they were synced and up, however still on the old chain. They have been provided with 2.1.1.1 addnodes and our bootstrap to ensure proper syncing this time.

At this moment I suggest not to, as any coins bought and sold on the old chain will be invalid on the new chain, and are likely to be lost when all exchanges have completed the update