That is because, you only have 109 eggs. The rest (up to the 400 or 500) is displayed as the cost in Diamonds (5 diamonds per egg).
This means that the cost, for you, for the hideout is currently 109 eggs + a lot of Diamonds (291*5=1455).
The more eggs you have, the less diamonds the objects costs... until you can pay for it all with eggs alone.
Hope that made any sense...