I think that's a very cost effective way of increasing your brands awareness, of course these sites individually to pack the consumer traffic that paid listing sites do, but if budget is an issue, then this free listing saturation is where I would first target.
The other thing about free listing sites is that you can usually get away with promoting your own site easier without breaking the rules, and your objective here it seems to increase traffic flow to your own site, your not really looking for a complete alternative to what you currently have.
It takes time, but time is something that every business has to pay, but cover your most cost effective options first if your budget is tight, then take a look at the results. From there you will see how effective the low cost saturation is and be able to adjust your marketing based on your results.