Hello!
I've worked both in web environments and in game development situations in the past, and I have a solid idea on how to do what you are asking.
I'm thinking of using the game engine Unity for quick and easy development. After the project is done, I could simply build the final version to a web page, getting the final result you desire.
Your specifications, however, are not very clear on many parts of the game. I'd have to ask you a few questions (such as how are the movements, how are the enemies, what kind of graphics do you want, controls, etc...) before giving a precise delivery date or ammount of money. However I'm sure we could agree to a reasonable value for both.
Sincerely,
Jean sidharta