As a self-taught marketer, I would say it is a better investment to use this money to build your own website and learn the basics from experience. From this experience, you can learn:

- How to setup a CMS (e.g. Wordpress)

- Keyword Research

- Content Marketing

- On/off-page SEO

- Optimizing for conversion rate

- Building and managing a mailing list

- Email Marketing

Also, being able to tell this story is much more interesting than simply saying: "I have this certificate from Udacity".