I would never estimate an effect under at least half a day.
My freelance rate starts at 95$/h.
So something simple like a campfire would be quick and cheap at 400$ or so.
If you want something complex like a destruction sequence with simulations, unique textures, materials etc we are looking at a couple of weeks worth so around 7500$
If you are after effects for an E3 moment you are looking at a couple of months, which might net you a discount for long projects leaving you in the ballpark of 20 - 40 K.
So it will vary a lot.