That is an impossible question to answer. It depends on how many of you there are, how long you’d be visiting, what sort of accommodation you expect, how many places you’re visiting, what you’re expecting for meals, etc.
All I can say is, Singapore is not a cheap destination. Even our budget hotels would seem expensive compared to those in other countries. However, most tourist infrastructure here, such as hotels, are online. If you spend some time researching them, you can easily work out a sum.
If you like some tips on how to save money while here, you can also take a look at this other write-up of mine.