I haven't seen it reported here but, in my game, the influence cost to create an outpost is not deduced from my stockpile of influence.

However, the cost does increase with each new outpost.

So let's say you're turn 10, have 120 influence, then you can create all the outposts you want until they start costing more than 120 influence.

Now, at turn 11 you have way more outposts than you should have and still have the 120 influence.

But, once you reach the ancient era and select a new culture, the cost start being deduced normally.