Wow. A bunch of depends and some ridiculous figures for a starter.
Realistically you can expect to pay $0.20-0.30 per like starting out in tier 1, if you manage to optimise and figure out what you'e doing, this can drop down to $0.02-0.05, lowest I got to is $0.0005. If you are getting them for $0.20 and you just started, it's a good indication, but I wouldn' base your performance on cost, I would base it on ctr and geo. If you'e getting targeted page likes with an ad that's doing 5+% ctr, that will only drop down in cost overtime. You should be cutting ads that are delivering below 3% ctr for page likes. If it's between 3-5%, give it a week, and as I said if it' above 5%, the cost should drop down. If it doesn', either your audience is super targeted and expensive or others still have better ads than you for that audience.
Hope that helps.