Tile coach has some pretty great videos where he tests the waterproofness of foam board vs membrane and membrane wins (albeit, marginally). The membrane waterproofing is thicker than the felt that comes preinstalled on the kerdi board. With all the requisite seam/corner/screw taping, I feel great peace of mind using membrane over concrete board, and it’s cheaper. However, for the ease of installation and ability to wet shim, kerdi board is a great option, it’s just very $$. For professionals who are trying to move quickly and save time, I think foam board is a great option. However for a DIY bathroom, you’re going to be going slow anyways, so why not save your money and get the best shot at waterproofing correctly (I emphasize correctly because there is a lot of room for error while installing your own membrane, so do your research). Remember, get the air bubbles out with a drywall knife, but don’t push all the thinset out, have the right trowel size, and overlap seams by 2”! More on reddit.com

Where is laticrete hydroban ? More on reddit.com

There really is no consensus. You're going to find people that insist that kerdi ( either applied fabric membrane over a drywall substrate or the Kerdi boards) is the only way to go and you're going to find people that insist that a membrane such as red guard applied over cement board is the best way to go. I'm a contractor that does many bathroom remodels. And I've used all three of the systems. My personal preference is the red guard applied over cement board. That is how I have been doing showers for many years. I've never had an issue and that's what I'm comfortable with and what I know. And after doing several cost breakdowns between all of the systems I do find that method to be the least expensive which helps lower my cost and maximize my profits. However the other systems are just as effective and work well. My suggestion to you would be to use whatever you feel like will be the easiest for you to work with. More on reddit.com

Dry pack or a mud screed is a excellent way to level the floor. As for the membrane I think your sources are confused. There is no membrane that will prevent your tile from cracking. There are membranes that will isolate cracks. Meaning if the subfloor happens to move and crack in a horizontal plane, the membrane will move and the crack will not telegraph into your tile. The size of your tile makes no difference in using a crack isolation membrane. Dry pack is not a substitute for a crack isolation membrane. Crack isolation membranes can be something like Laticrete StrataMat or a liquid you roll on like Hydroban. Both are definitely less than $2 per ft. You would place the crack isolation membrane over the drypack. The bigger question is what is your subfloor now, wood or SOG? More on reddit.com