You could pay for 200-300 MS Teams seats for a decade with that kind of money pile, or a F100-sized Oracle database instance.
I went through the whole slack->mattermost pipeline a very long time ago to avoid (at the time) Skype for business and the initial rollout of Teams.
It turns out we wasted a lot of time trying to be clever and not pay the devil for his services. Unfortunately, there are some proprietors in the space who occasionally make the devil look like a saint. I'd rather do business with him than return a call to a "at least it's not you-know-who" company that fucked me this hard. The devil is brutal but not this brutal. Larry Ellison would at least have his sales people buy me a fancy steak dinner first.
I went through the whole slack->mattermost pipeline a very long time ago to avoid (at the time) Skype for business and the initial rollout of Teams.
It turns out we wasted a lot of time trying to be clever and not pay the devil for his services. Unfortunately, there are some proprietors in the space who occasionally make the devil look like a saint. I'd rather do business with him than return a call to a "at least it's not you-know-who" company that fucked me this hard. The devil is brutal but not this brutal. Larry Ellison would at least have his sales people buy me a fancy steak dinner first.