Yes, it is effective. But as with anything, be cautious. I suggest you test it out.
It's because you have to define the age target, location, preference and such.
You have to consider/decide if you want to promote it to a specific target market, people who like your page or solely friends of the accounts that already liked your page etc.
The amount you pay depends on how many days you want to run the ads for. It could be for a day, one week or even two weeks.