That ish is tough from what I know. The start up costs can very but the profit margin is low unless you product gets popular. Doing pop ups in a place like NYC or SF will raise your profile but if you aren't in a fashion forward area it will be more difficult because consumers in the area won't adopt the style until they see it on TV.
Buddy of mine tried getting a line started months ago, paid me for some graphics, found a good deal on gildan bulk orders, had a local manufacturer but he just gave up trying for some reason
i'll pm youyou got a website or portfolio of your graphics?