Hi,
I am already into Biz opp, Casino And Nutra. What other verticals should I focus on? I tried Payday loans couple of days ago. Got some conversion but very hard to turn green. All big guys sitting on top with $10+ CPC.
Dont know how much you will be able to keep traffic going for these verticals on Adwords.
Software/Background Checks/Travel are good options for search traffic.
Everything works with search, its just a question of compliant offers and your ROI (as you mentioned, finance is difficult with all the heavy hitters).
Isn't "focus" about focusing on just one thing? Maybe you should consider focusing on focusing on focusing...
I've been focusing on dating for 10 years, and even that has many niches.
Yup, anything can work on google search traffic. It's the best traffic that exists, so if it doesn't convert on search, it won't convert anywhere
The high bids are a problem though, adwords is the most competitive market place in the world, so if something converts well, related searches will be very expensive.
Courses, ebooks in the right niches ... this can work well too.
Focus on finding a niche with cheap enough clicks. As everyone else said, the cost can be a challenge. Of course, there are ways around that. 
Focus on 1 thing first and get that working rather than trying to do 1000 topics.
Search is good, however as others have mentioned the cost is high (traffic is good quality) make sure the offer is compliant and you work on specific keywords at first and creative ad copy.
That creative has to display a competitive advantage from others on the listings to get your potential buyers in.
Then you work from there on the landers.
Happy hunting
For lead gen offers run on SEM, do people usually use just a form fill lander? Or is it a deeper funnel with multiple landers and/or email marketing?