Are you referring acquiring clients for your agency or customers for your clients? I assume it's the former as the later would obviously vary greatly by clients. As someone who spent 7 years on the agency side including identifying, pitching, and winning new business as well as currently on the client side (being pitched), I would say networking is going to be your most effective tool from both getting your foot in the door and not breaking the bank. Go to conferences, events, etc but don't buy a cheesy sales booth. Just make natural conversations and when appropriate, chat about how you can help and present it in a way that minimizes risk for the clients (first 30 days free, cancel anytime, etc). Just don't be too salesy :)

I have a lot of experience in this area especially on the brand side knowing what I'd want to hear if I'm being pitched. Feel free to schedule a call with me to chat further on this!