3 - The typical business plan in the US calls for $10,000 per developer month, which covers all the costs of employment.  Once you have a firm grasp on the number of months and number of people involved, it is a simple matter of multiplication.  

Getting an accurate number for both of the two factors can be difficult,but for a Habbo-like game my gut-check reaction says $5M would be a low price just for development, you'd probably need another $5M for marketing and another $3M for support for the first year.

For a hobbyist game that mostly works okay for the few people who play it, you could probably cobble something together in a few development months.

3 - The typical business plan in the US calls for $10,000 per developer month, which covers all the costs of employment.  Once you have a firm grasp on the number of months and number of people involved, it is a simple matter of multiplication.  

Getting an accurate number for both of the two factors can be difficult,but for the scope you are talking my gut-check reaction says $5M would be a low price just for development, you'd probably need another $5M for marketing and another $3M for support for the first year.