professional software developers who know their own skills well and have a well written design document still get software estimates wrong the majority of the time. Trying to accurately predict the cost of a software project is a fool’s errand.
Game development isn’t cheap. We spent 1.5 years developing the game and hired multiple art/sound contractors to make GDT but that doesn’t mean that any random other team would spend the same amount of time or money.
Some people create great games in a game jam or over the weekend, other companies spend decades and multi-million dollar budgets and never ship a game. There is simply no way to give a blanket estimate.