Top Three Mountain EBikes
 

Any opinion on the best mountain e bike (especially for durability) and ride
also what the situation using them on hard pack sand at the ocean
how bad does the salt air and water damage these bikes
Approximately how much do these bikes cost to maintain

What bikes are you looking at? What sort of riding do you plan on doing? Bosch, Brose, Shimano are good quality motors that are easier to service and work with.

Salt water will damage your bike but if you keep up on maintenance you will be in better shape.

An e-bike doesn't necessarily cost more to maintain or have more problems then regular bikes but you may end up wearing out chains, cassettes, brake pads and rotors a bit more often. The cheaper stuff will generally wear out more quickly and will have a whole host of other problems.

The term "mountain bike" covers a lot of ground.
To receive better suggestions, you might want to specify the following:
your budget,
your weight,
amount of load you plan to carry on the bike,
type of riding you plan on doing, distance, speed, duration, etc..
type of terrain you typically ride,
weather conditions that you typically encounter, sub-freezing temp. possible?
All of the above will determine the parameter of e-bikes that may suit your needs & possible cost for maintenance.

We should have a "sticky" for individuals who ask about the "best" bike. It could incorporate the ones above, some that DW proposed in another thread and others like can you charge at work (commuters, obviously), do you need to carry the bike up flights of stairs etc. BTW, I was n my LBS about a month ago and there was an eMTB with a new Shimano for repair. Shimano said they would have parts to effect the repair in May.

Yeah a common problem these days with a lot of manufacturers. Quality stuff and the cheaper stuff is all having supply issues this year thanks to COVID. However considering Shimano is the largest (or at least very close to the top) supplier of bike parts to everyone they are certainly magnified but what can you do. It is not like they could have planned for this year and the bike boom. Nobody knew how bad this would be in late 2019 and even early 2020 we had no idea it would be this insane.

A sticky could be handy.

VB, you're so correct. As a different example, a year later 3M still can't produce enough N95 masks. Considering how crucial the masks are, bike parts are of much less importance.

The first thing the sticky should do is drive home the fact there is no such thing as "best".

Wanna ride a bike on the beach? Luna Fat Babe checks a lot of boxes.

https://lunacycle.com/babe/

Fat tires, belt drive, no exposed gears. plenty of power, decent sized battery. It is heavy but anything with fat tires is not going to be light

There is "best" when specific parameters are given for specific person; but that may not be best for everyone else across the board.

Yep, define best and one can have a conversation. But I've read too many internet threads with people talking past each other that the "best" advice is to avoid any conversation asking what is the "best".

I don't think avoiding any conversation is a good strategy when someone is asking for help; maybe just ask the person to be more specify of their needs.