Advertising needn't be expensive, but it does have to be thought through. Defining and narrowing your target audience will enable you to concentrate what budget you do have for that sector, maximising possible return.
Executing campaigns to a small, well defined list of prospects enables you to create, produce and follow up an in depth 'mini' campaign that can be well managed. More importantly, it enables you to track and measure the effectiveness. Results can then be adapted and refined for the next campaign.
Keep an eye on the local job paper advertising vacancies for company decision makers/purchasers responsible for hiring you (freelancers). Phone up later to find out who filled that job - you then have a reason to write to that person congratulating them on their new position with a brief outline of who you are and what you do. New staff often want to bring in their own suppliers as a fresh outlook and as a stamp of authority for them.