Newcastle's Ameobi is England's record loan signing
And the final figure for the striker, who has not scored for nearly 18 months, will approach £1million if Stoke go up via the play-offs, with a bonus due to Newcastle on promotion.
But City chairman Peter Coates said: "We wouldn't want to look back and think we haven't had a go. We have done a deal and taken that risk. There are no guarantees but we're trying not to miss out."
In addition to the down-payment to Newcastle, Stoke will also meet the player's estimated £25,000-a-week wages until the end of the season on May 4. He will stay at the Britannia Stadium if the club reach the play-off final on May 24.