Hi,
I agree with both Cory and Brian on this one - you might be able to start off by yourself, but it's very likely that you will need some guidance later on. And I'm not just saying that because I'm managing other people's FB campaigns or do coaching.

We don't know much about your business, or which country it comes from, but the main thing you have to know is the cost of advertising in the US - it's significantly higher than in the rest of the world, reaching the CPMs of $20 or even $30 and more for some very specific audiences (that's $20+ just for getting 1000 impressions).

That means that a 'small scale' campaign in the US can cost up to 10 times more than in South America, Eastern Europe or South East Asia, for example. If you want to do that in the US and run some split-testing to analyse a few audiences, offers and ad designs, the bare minimum will probably be around $1000/month on ad spend.

Talking about agencies, some of them take a fixed fee per month, others charge a percentage from your total ad budget - that can vary from 15% to 30%. So you will have to ask yourself whether it's worth for you to experiment with ads, or if it's better to hire someone to help you, when the cost of a mistake is very high.

If you plan to spend $1000/month, and we can help you improve your ad campaigns by 10% after a single call by helping you with the right setup, audience selection, split-testing and optimisation... you're already in a positive. :)

I've had some great results from helping businesses optimise their Facebook ad campaigns - let me know if you need any help with yours.

Cheers!
Adomas