How many coins does it take to fully expand?

My estimates are around 4-5 million coins, is this possibly close to how much it actually costs to have a fully expanded farm?

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Why I am asking this is because I'm saving up all my coins to expand the rest of my farm all at once, or within one go.

I'm wondering how much coins I would need to save up.

I almost have 1 million coins, or will by tomorrow.