The title says you'd like to "create" a site. And no where did you mention anything about building the assets : ) I mention this because it's important to properly categorize the web publishing work ahead of you: create, host, market, secure, and maintain your digital property--just to name a few. And if you rely on a publishing host/service, you will never "own" your digital property. So keep that in mind. If you ever need to migrate from one service to another, it could be a pain. For most, it usually is.
1. What is the cost to set up/host a site?
Depends. If you can reduce digital assets to static form, you can host the site on AWS S3 for $3-$15/month. If you need a full-blown dynamic site, with web-app behavior, you can use serverless cloud services to save quite a bit of $$$. You will only be charged for what you use. There's no running meter to charge up the CC. You should invest in someone doing the initial work for you, learn how things work, then try to learn how to maintain things on your own. If not, you can use managed apps with any typical host (Linode, Digitial Ocean, etc). Their services abstract the complexity so you can point-and-clickity-click your way to noob site building. Just keep in mind, you have almost 0 flexibility for customization. And when you decide to customize--because you will---you'll pay out the nose for some hipster to do side projects for you. This will increase your costs over time, because when said hipster is too busy partying in BKN and you need something done, the next hipster working on your site needs to understand all the L33t cODe the previous hipster wrote before he/she/it/they gets any traction in the codebase. Hosting plans vary, but most are affordable. You will only pay $$$ if your site goes main stream.
2. How do you drive initial traffic to a site?
Depends. Who is your target market? What's the demographic? Generating traffic can be as easy as paying Google. OR you can establish a youtube channel, build up followers (~150K is good, 1M+ is better and youtube sends YOU a check every month), then send followers to your site ("click the link in the description!!"). So many ways to drive traffic. They key is not to rely on one method and wait for site visitors to flood your host.
3. What else should I know?
LOTS. But you have to start somewhere. amirite?
PS:
I know this was a pre-covid thread. Adding my opinion just in case it helps others. If anyone disagrees with my opinion, fuck it--neg me!