If I am to look for streamer to hire, the minimum subscribers I would consider will probably more than 200k-300K and will still negotiate about the price down to minimum also.

RiiSki has less than 50K. He is less popular.
I don't think that you'll be able to hire someone with more than 200k subscriber and offer minimum amount for their service and collaboration. I don't even think a normal streamers who stream games will accept a minimum offer. We must also think that gambling streamers doesn't receive as much viewers as normal games.
Upon checking to RiiSki, I've seen that most of her videos received more than 1-2 thousands viewers per video on her youtube channel. I think that it's sufficient enough to be qualified for a collaboration and it has potential to provide more clients and gamblers to the platform.