It truly depends on the scale of the project. If it is a simple site and nothing else, then it shouldn't cost you more than 0.2 BTC. However, if it a large project like all those new ICOs then it would cost your quite a bit. From advertising to project managment and design, everyone needs to be paid and that is going to take a lot of Bitcoin. I have seen some websites, like gambling sites or trading sites, keep up a signature campaign for years. Do you remember Bitmixer? That project was huge and highly successful. I would say that it paid out more than 5-BTC per week.

So if you tell us the scale of your project, it can help us answer this question a bit better.