A budget is not just money

And if you have absolutely no money to spend on marketing at all, then your budget is not going to be measured in money but in hours.  If you know that you’re going to be doing everything yourself instead of paying for others to do it then you need to decide realistically how many of those hours you have got to give.  If you are going to have to learn how to build a website yourself then that needs to be added into your time budget, and you have to make the same budgeting decisions: before you give up 50 hours of your time budget to build your own e-commerce website, can you test your idea first using Facebook marketplace instead?  If you have identified that 10 activities will get you customers but your time budget can only afford three, which three are likely to get the best results for the least hours?