1. Print-on-Demand Products: Use a print-on-demand service to create and sell custom-designed merchandise such as t-shirts, mugs, and phone cases. You can design the products yourself or outsource the design work for a low cost. With minimal upfront investment, you can set up an online store on platforms like Etsy or Shopify and earn passive income through sales.

2. E-book Publishing: Write an e-book on a topic you're knowledgeable about or passionate about and self-publish it on platforms like Amazon Kindle Direct Publishing. With a budget of under $50, you can create a professional-looking cover using design tools like Canva. Once published, your e-book can generate passive income through royalties from sales.

3. Affiliate Marketing: Start a niche blog or social media account focusing on a specific topic or product category. Sign up for affiliate programs with companies that offer products related to your niche and promote them to your audience. You can use free blogging platforms like WordPress or social media platforms to share affiliate links. By generating sales through your affiliate links, you can earn passive income through commissions.