Importing from SMF
There is an importer for SMF2. It appears to import avatars and attachments, but not polls or PMs. It has not been updated since the move to the new Markdown engine, but that probably does not matter. Most people run importers by first installing a development environment.
To provide a quote for the import, one would need to know more about how many total posts and users you have.
What about hosting?
$100/month is about paying a team of professionals around the globe to keep your site up and have the features that you desire be on the short list of features to be added to Discourse.
Then you are a good candidate for self hosting. See install-cloud for more information. My $99 install page also has a FAQ section.
It’s likely your database is big enough that you’ll need to go with a 2GB ($20/month) server (or Digital Ocean “droplet”). The price on other hosting companies will vary, of course.
It’s easier to run Discourse on a server by itself, so I’d recommend that you start with Discourse on some other server and then deal with moving off your Windows server and then to your Discourse server as a separate task.