Most decent hosting providers give detailed breakdowns of their service costs (servers/cpu-slices/bandwith/transfer-rates/limits/etc) so if you are able to appr

Most decent hosting providers give detailed breakdowns of their service costs (servers/cpu-slices/bandwith/transfer-rates/limits/etc) so if you are able to approximate your usage levels e.g. by comparison to the patterns of other established similar apps/companies, you can do a good job in calculating these costs. Even not knowing your usage levels, you can make reasonable assumptions and hence choose appropriate services with fixed costs and work on that basis. Amazon Web Services, SliceHost, and the like are particularly good if you do not know how your service/app will perform over time as they allow you to scale with ease compared to other more traditional hosting solutions and although more expensive in the long term (i.e. buying dedicated servers are cheaper), is cheaper in the short term and actually makes creating early projections much easier.