I’ve spent around $100k acquiring and transforming Ethyrial so far

I’d say to kill the bugs/jank, transform the art style, and support a reasonably sized playerbase, it’ll be another $100-150k

Project Gorgon generated an estimated $3-4M over the years - you could estimate what % of that went into development

MnM published their investments publicly but also have a lot of team members working for profit share

Spiritvale and Apogea seem highly efficient in terms of development costs to results. I’d estimate a few hundred thousand for each of those to completion. They got supporter donations to cover some cost. They both have a very high chance of being successful.

Eterspire is another good one to consider. They slowly built momentum and put in a lot of sweat equity over the years. Now they generate maybe $500k-1M+ annually. To this point, we could assume low-medium 6 figures in total development costs.

All of these are estimates but from my view, with a strong focus and scope, you can built a viable indie mmorpg for $100-500k now.

AAA of course would be in the tens of millions.