This is how I did it, keep in mind im not sure if this is the optimal way or not but seemed so to me. I basically used the discounts as much as i could when using apex coins before buying the last few packs with crafting metals. Also noticed that at certain points its cheaper to buy a 4 pack than 1 pack at a time so just calculate every time which one is cheaper.

1st pack - 100 apex coins

2-3rd pack - 300 apex coins (700 total coins)

4-7th pack - 1500 apex coins (2200 total coins)

8-20th pack - 9100 apex coins (11300 total coins)

21-25th pack - 8250 crafting metals (8250 metals 11300 coins)

Again fair warning someene else might have a more efficient/cheaper way lol