There is no magic bullet here. But some of the new targetable ad channels are pretty affordable. Facebook, LinkedIn. I would test $100 and see what results you get. You also want to use content marketing and tie it to SEO. Optimize for "How do I find a good accountant" and provide top 5 tips on what to look for in an accountant. Good content will also draw traffic on Twitter and Facebook. Contests are also a good way to draw people in.