I'm a starter on the online space, trying to promote some product, but I don't have enough money yet to run my campaigns. How do i get a really cheap advertising agency to promote my product?
The answer here is probably not to go for an agency.
Find a freelancer or consultant with the neccessary skills to work alongside you.
If you have a marketing plan, note down your name against any tasks you can do yourself and commit to completing them. Everything you can't do - find friends, family, interns or freelancers to help with.
If you haven't got a marketing plan, find a freelancer to help you create one as your first step.
