Suppose today you started with no money in your pocket because you spent it all on product development. How would you market it with zero budget?

Easy. Assuming you have product to market fit, all you need to do is figure out where the people for whom your product solves a problem are 'hanging out'.
You then need to come up with a simple plan to get them used to the idea that you or your product can solve their problem and then introduce them to the product.

None of this costs any money. In fact, even with companies that *have* money, I encourage them to use these routes over things like advertising because it's far more potent.

Hope that helps you understand better, and gives you some clarity (no pun intended).
If you need any further advice, feel free to call me. I should be able to help clarify everything in less than 30mins.

Find distribution channels and sell, sell, sell. If your selling a retail product see if you can sell it on Kijiji, Craiglists, Ebay, or Amazon.

I've worked on several startups that didn't have funding. We worked with large companies and basically gave the platforms away in exchange for their feedback and use of their testimonials. We also utilized content marketing to discuss industry challenges and connect with industry experts. Over time, that network we built and the customer base always paid off.

I've had a similar experience with my own brand and also helping other brands with the same dilemma. Two things off the top of my head that have worked very well are:

1. Build up your social media platforms. If you do this yourself, there will be no cost - just your time but you will be on your way to building advocates for your product. When I launched my company, I had to curate my audience on Facebook, Twitter and Instagram. This was time well spent and we gained great insights and sales.

2. Identify other companies that might benefit from a marketing collaboration. For example, with my start-up we too spent the majority of our funds on the product but then approached like-minded brands to work with. The result was that by using their network of customers and marketing initiatives I was able to promote my brand and gain direct sales. Which brands did I align with? Quiksilver, Oakley and Audi of America were just the first 3. I didn't spend a dollar and they invited my brand to communicate to their customers. And yes, i still work with them to this day, my relationship has only become stronger and they now include me in some of their efforts throughout the year.

If you're interested in learning more about how to market a brand with a zero budget, I'd be happy to join you for a quick call to help identify some potential businesses you might be able to collaborate and expose your product to.

This is the most common problem I deal with as in our Mentors 2 inventors group. Inventors are notorious for spending too much time and money on prototypes and product and not enough on business or marketing. In my experience launching over 250 products, zero budget is not going to get you anywhere. Small budgets don't work either. Speed to market is essential. My suggestion is partnership. Find partners who will market for you. Be prepared to give them a very large cut! Remember that a product is nothing if no one buys it. The power is not in PD and invention but in who has access to the market.

In my opinion you don't need marketing yet, you need sales. You have a nearly zero cost channel called the telephone and email (get opt-in first). LinkedIn if it is a B-to-B product. Just start selling it and get a few customers. Build on that, learn from it, sell a few more. Once you have a good product, take happy customers and get referrals and/or testimonials. THEN start marketing via social media. If it's a fantastic consumer product with large potential customer base, you might actually be able to start to grow. If not, you probably need to get $ for marketing ASAP.

Ditto to all of the above. Since you say it's a product, rather than a service, I'd also find some bloggers who do product reviews in your niche and pitch them about reviewing your product. Also, another way to get publicity can be to join services such as H.A.R.O. (Help A Reporter Out) and Pitchrate and respond to the queries in your niche. (They're services where reporters post inquiries when they're looking for experts for stories they're working on and products to review.) BUT--and this is a major one--before responding to queries, really learn the proper way to pitch a reporter, and be sure you have an online media kit containing the things they'll actually need, in the form they need them. Journalists who use HARO and Pitchrate are pros who expect a strong level of excellence, and there are very specific ways of how to approach them. I can show you how to do this if you'd like to schedule a call.