We can collect 600 coins in each time window.
We start with 110 coins. The island is up for three days. So we can get 5510 coins in total. Coins we collect from watching trailers are not included.
The map shows the cheapest way to get all dragons (skipping one is not possible) and all artefacts. We do all fights on the way. We dont buy out fight fields. That would make it more expensive.
Here are some numbers:
To get Carribean (we collect the first artefact on that way) we need 1160 coins.
To get Bull we need 5340 coins.
To get the second artefact we need 5460 coins ( until this point we dont need to buy coins).
To get the third artefact we need 8420 coins.
And finally to get Sandcastle we need 10972.
So if we dont miss a collection we can get the first two dragons and two artefacts for free.
IF you don`t go for the artefacts you can save 210 coins by using the way at the bottom to reach Carribean. But that would not help much imo.

Many thanks, Bettina ))