Diablo 2 Resurrected anywhere cheaper?

Nah, you won't really get Blizzard keys for cheaper anywhere.
I've been looking for Warcraft 3 Reforged for a discount but haven't found anything so I assume the same is true for Diablo 2 Resurrected

Is it actually decent enough to spend time on? I have no trust in Blizzard after W3 Reforged

No, don't do that with Blizzard games, it will get revoked.

I'd stay away from key shops in regards to any Blizzard or Battlenet games if I were you.. Your best bet is to get it through the Battlenet (online) shop because there won't be a physical disc release this time around.

Here is more info about D2R and where you can purchase it.

there's no chance to get it cheaper

i bought it on official store from blizzard. it was on sale. not anymore.