It would move the buy price to $2000, but in theory the sell price wouldn't be moved and so there would simply be a large margin until liquidity improved.

If no one is willing to buy a bitcoin for $700 right now, there's no reason to think anyone would be willing to buy a bitcoin for $700 even if you were offering $2000 for any bitcoins on the market. Of course people aren't rational and you might catch out people ignorantly trying to follow a graph they don't understand.

This is in part why it is irresponsible for exchanges such as mtGox to report a single "price" for bitcoin, they should always report the current prices as a tuple of (Offer, Bid) prices.