With all the guardians of the rift perks, and the new blood alter being able to use rune essences on.
How much cheaper could they get, does 200 sound likely?

Could I soon stop bursting and just go to barraging for slayer?

you should already be barraging. the price change probably won't really make that much of a difference.

Maybe I am being unreasonable with wasting time, how much more would I end up paying on an extended task that I make like 700k on?

honestly i dont know exact numbers, I just know when I barrage something like nechs, im still making good profit and getting a shit ton of exp.