IP to Blue Essence

I did the thing where you buy champ shards to convert ip to BE, but should I keep the shards that i have mastery tokens for? better question- will the cost still be 500 and 600 BE for level 6 and 7 mastery?, because if it stays the same it'll be worth to disenchant, so it gets the 6.5 multiplier, but if the cost increases, then it might not be worth.