On the latest builds for Redstone, I have seen no way to obtain it. I'm still on a limited data plan for the next 30 days, and it is something I have to watch very closely. For now, I keep it on metered connection and just travel to town a couple of times per week to put it on free Wi-Fi to update builds. Last time I tried to do one at home, it used up 2.7GB of data, and it ate up all my rollover data. I ended up with 500MB to get me through the last 7 days of the month. I pretty much had to turn it off after that.
This is something we definitely need to open up feedback about and let Microsoft know that we need to have the download size for updates, builds, or whatever else is coming down the pike. I also would like to see update size in the Store when there are updates to download before I click the download link. It used to be there and has been removed.