For an open source business model consider "open core". Open source the core engine, and charge for additional features. I would recommend SQL Server and Oracle be paid enhancements as companies in that ecosystem are used to paying for tools. Keep postgres/MySQL/SQLite, etc open source as they are tools that developers using open source would be using.
Then charge through the roof for the additional features. I recommend at least two tiers: a lower price for access to the premium features, and an "Enterprise" tier which adds in support guarantees.
Don't do a one-time payment either. Make it a subscription to receive new updates etc.
The low tier could be ~$50/month, the high tier can be "contact for pricing": but if contacted start the discussion at $1000/month. Then allow them to negotiate a lower price, perhaps with your absolute floor being $500/month.
This is all armchair advice, so take it with a grain of salt. But I hope it is helpful.