Of course nothing is free. When you are not spending money, you are spending time. If that appeals to you then following activities can be done spending no or little money.
1. Blog Writing: You will need some writing skills. Do it once or twice a week.
2. Social media engagement: Create profiles on facebook and twitter and engage users there to bring to your website or physical store.
3. Link building: It is a good tool to increase your search engine rankings. You can build links by writing linkable content on your website so that other will link to you or by posting valuable comments on blogs and forums.
4. Video Marketing: Create videos with instructional content on your topic and post in online. It is easier to get searched for your keyword.
So if you are on a budget no reason, not to start marketing your brand online.