Cheapest method to gain facebook page likes ?

I'm planning to spend a few dollars on facebook ads, and I want to use the best method to gain page likes.

What should I choose:
1. Use a viral post to buy interactions, and then invite people who liked post to like my page
2. Buy page likes

In my exprience, buying likes is pointless.

depends on what kind of likes you want.. cheapest are the ones you buy from smm panels.. but those aren`t very reliable.. they won`t help with page interaction at all.. I would encourage you to use viral posts to boost page likes.. more expensive but real people that will like future posts of yours

quality content!
or you can just buy run an ad campaign aimed for a group likes

you can advertise your page into other related pages, just pm them how much,
in our country, $40average per month, 1-3 post per day.

Buying likes will put your fb account and your fb page in risk of getting deleted/unpublished since fb has become really strict lately.
I would recommend to stay away from buying fake engagement as it would completely screw ur fb page!
Try to find viral videos that actually went viral from other pages and use fb group to grow your fan base to at least 10k, then focus only in well performing posts and posts that you think or you got the feeling they can go viral. Use fb ads on your viral posts > invite everyone who liked your post = Page Growing.