Players about to hit level 20, thinking of letting them spend excess XP above 20 for mythic destinies. How much XP per feat?

[Ryangwy]

For context, I've been running a Menace Under Otari -> Abominations Vault + Troubles in Otari -> Extinction Curse (Book 4 onwards) campaign with XP and naturally my players are about half a level ahead of the curve (to be exact, they are entering the [ISPOILER]Vale of Aroden[/ISPOILER] at level 19 with 500 XP). That's been all fine and dandy up til now, but they're going to hit level 20 soon and will have no reason to chase after XP anymore and my players love chasing after XP.

I'm thinking of letting them buy mythic destiny feats for a set amount of XP, which should hopefully keep them engaged, but how much XP should a feat cost? And, for that matter, which mythic destinies are a good idea? I'm not going to give them mythic points, which will make things extra messy.

[YuriP]

AoA last book starts to gives some permanent boosts at the end of each of moderated or higher encounters in the lvl 20 part. You could do similar based in this and give to them a feat for every 80XP or more. But notice that you probably will need to compensate this in the final battle maybe turning the last boss mythic or may end with the players killing it too easy due the extra feats.

I don't remember the last part of Extinction Curse but first check if the AP isn't already giving them boost rewards in the last level too. Maybe you not need to give them anything extra.

AoA Broken Promises boosts spoiler:

Spoiler:

Each node that the players purify basically killing the enemies or solving its enemies question for fake Ilgreth and the fake Mengkare gives boosts like:

Permanent improves the success grade of saves vs things that turns them controlled.

Permanent resistance 20 vs fire

Permanent improves the success grade of saves vs things that gives them drained or do negative/void damage.

Give the ability to cast Truesight once per day.

Improves an attribute by 1 (ignores partial)
The last boss gives nothing because it's the last fight :P