Seeking to build a game prototype for online access!

Wanting to build an online game without an upfront phone app or a need to download initially. Browser ready game at first. A phone app and such later. Also need help to validate a demand for the game. You got any ideas for an MVP-minimum value product. Not ready to buy your service yet but would like a cost range or an answer to some basic questions from you and/or your team who would have to develop this. Let me know! -Don