Milky Way / Timelapse Lens for a Canon 6D?

Hello everyone! I'm trying to figure out what my next lens should be. I mostly shoot timelapse and love shooting the milky way. I was previously shooting on a Canon T3I and have since upgraded. I used to use a Rokinon 14mm and loved it, but after leaving it out one night in Hawaii and the sprinklers turning on it has gotten some water on the inside that I can't get out

Anyway, i've upgraded to a 6D now and am looking for a new lens. The two things I didn't like about the Rokinon were that it clearly wasn't weatherproof and I couldn't attach a filter to it. I really wanted to experiment with an ND filter for some fun daytime timelapse, but that wasn't really possible with the 14mm. The other lens i'm looking at getting is either a 24-70 or a 24-105 for a sort of all around lens and then i'll pair it with a really wide lens for my timelapses / milky way stuff.

What's your budget? I don't own any of the Rokinon lenses and was surprised to read it didn't have a filter thread. (Is that true of other models, or just an issue with the 14mm? Canon's 14mm doesn't have threads either because it has a permanently attached tulip lens hood.)

There are a few 24mm f/1.4 lenses on the market (which is why I asked you about budget). At f/1.4 you collect 4x more light than an f/2.8. While the 24mm is a longer focal length, it's less than double the focal length of the 14mm. When you net it out... the 24mm f/1.4 can still collect quite a bit more light than the 24mm ... even after compensating for not being able to run the exposures as long.

To keep noise under control, you'll want to be able to maximize how much "signal" you can collect. (maximize the "signal to noise ratio")

The rokinon 14mm has a permanently attatched lens hood so it doesn't have a common filter thread.

I'd say my budget for a lens is somewhere under $600 is possible. That Rokinon is super affordable and can be found used for around $200, but id love to tinker with filters.