Also you could hustle some of the service providers.
Example...
1. Find someone who claims they can get you an X amount of likes.
2. Add them on Skype and sound legit telling them if they accept PayPal before even talking about the likes service. Be polite and professional.
3. Tell them that you're hesitant since you don't have any proof they can get you the X amount of likes. Tell them that you have a big project and that you're looking for that one person you'll pay for the next couple of months for their services if they are good. Most providers are looking for a steady income and this will soften them up and give them an erection.
* Important, make sure the person offering the service isn't too popular or is just trying to break into the business. They are desperate enough to fall for this game. People who have proof and are established will simply link you to their work and that's it.
4. NOW, tell them you'd like to invest some serious money because you're looking to get around 10,000-20,000 likes (if not more). NOW, they'll look at 500-1000 likes like it's nothing. So before you "purchase" the 10,000 likes ask them politely if they can prove themselves to see if it works with your page. Usually they'll offer 500-1000 for free if not more. (I've gotten around 2,500 from a single person without paying a cent)
5. Wait for the likes, block/delete them from Skype = profit.
You can do this to a few providers all over the web so you'll get thousands of likes for free. Also you could always hustle them for more... claim the likes are fake/ or look fake and that you're not too satisfied/convinced. They'll make their best to prove they can get real/ "real" looking accounts and add even more likes. Also you could keep them as friends for a while telling them you are convinced and that the project will start in a few months. Until then you can befriend your way to more likes.
It sounds more complicated than it really is. Be polite, use your smarts and it'll be fast and easy.