You don't need to pay. Ask if you can put up posters in your local shops, library etc. Do A5 sized fliers and get them into doctors' surgeries, dentists' waiting rooms, hairdressers, local garden centre, local clubs and societies, community centres etc. etc. Put posters up on your gates/boundary walls/fences. If your local Freecycle has a Cafe group, post an ad there. If your council has a website with details of allotments, ask them to say that there are plots available on youir site.