It’s not much different than the investment of a small 3-5 page website. I think $1000 minimum to start. It’s a extremely niche skillset. Setting up the bots, role architecture, etc can be time consuming. Then developing and typing all the processes and procedure, throwing in training.
I think most people would underestimate this project.
It’s probably not worth as much as your hoping for “if legit” same thing with social account. Now if it belongs to an actual brand, with site, socials, etc and real traffic then there’s potential. You can ask around in forums for sites like empire flippers that deal with buying and selling digital businesses