We had the same experience. We were able to get a "like" for our page under 10 cents (In Indian market). Number of likes grew from 500 to 5000 in matter of days. But drilling bit more, it seemed like most of these people were having hundreds of likes. As a business owner at the end of the day it was hard to quantify value of these likes. We waited more, and started measuring engagement of these users for our subsequent wall updates on our pages. Results were disappointing. Engagement of people generated from "organic" likes was 10 times higher than the one generated from paid advertising. We also found that very few of those 5000 people ever engaged with our page in subsequent weeks.

Bottom line: We were happy to generate 5000+ likes with little money, and that helped us look like more legit and popular business. However, real value of generating business from these ads was minimal.