I've setup a new site called; www.comparethebiz.com and I'm looking for startup or small businesses to sign up, any advice please?

I read about 2 things: drive large traffic and expand to bidding platform.
What you should be doing is the million dollar question: how can I spend $10 to get a sale and profit $20 from it.
Notice: sale, not traffic or user.
Like you mention, there are tons of ways to get traffic but you don't want 15 year olds from India by the million visiting your site. What for, right?
The way I would approach it is via trial and error. What works for your competitor may not even work for you.
But please, never go on all fronts. That never works. Every startup with limited resources that I see create a Facebook Page, build a blog, doing SEO, email marketing and so on, they fail.
I can take a call with you to understand better what resources you have and give you my opinion on picking one channel to try for X amount of time, what to do, what to expect and how to track success.

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.