I would recommend being behind a well configured hardware firewall to start with, which could add to the cost considerably (if you're thinking of going for a cheap £50/month dedi). If you really need the performance or ability to configure things to your heart's desire, then dedicated or virtual dedicated is the way to go. However, if you're not used to managing Windows servers and hardening them and the websites you're running at important to you financially - it may pay to spend a little extra on a managed service.