Most would probably recommend cloud for smaller organizations, and that also avoid any startup costs, and requires less in-house knowledge of how to configure servers, etc. However, none of the online licenses would include an internet site. To be clear, I'm not recommending an on-prem sharepoint server for this, and instead would recommend a product that is designed for internet sites, as in, not SharePoint. Project Server is licensed separately. Before going the project server route, I'd recommend ensuring that you need it, as the product is only useful if you have people who know how to use MS Project. There is a free (included in the license) product management tool called "planner" that is part of office 365 which many people like. (Though people who know how to use and enjoy MS Project will not enjoy planner as much, as it's a lightweight tool).
Regarding cost, check out the options page here for the different small business plans, which run between $5 and $12.50 per month, per user (and include email, intranet, and other services, but not project online which is licensed separately).