You can easily run Discourse on a $5/month Linode server (other companies have similar plans, but I’m familiar with Linode). Start with something like that and only look at bigger options when you really need it.
(Of course that’s not pricing in time to run the server. It doesn’t take a lot once it’s set up, but if you don’t have experience managing Linux servers then it may be better to choose a managed hosting option. Discourse themselves offer hosting, but so do other companies.)