1) Be clear about what you want: know how crisp you want your site to look, how much colour you need, how attractive the banner would be etc.
2) Find the right person: the right person is not the guy who makes websites for Oando, because you're not Oando. The right guy is the one who can LISTEN to you and design the landing page or banner or code the site for you at your price. Its very important. Don't give it to a superstar because you think they will do a good job. Superstars have nothing to prove and often times, they won't go over and above to please you.
3) Have reasonable targets: so you've found your guy, good! Give him or her reaosnable targets to work with and make sure the freelancer is evaluated appropriately. You can create a Google doc where he/she would fill in 'done' at the end of each target or something, depends on what you want.
4) Where do you find them: You can find them all online! Try dumping Google for a change and use Twitter to search. Cc some common brands that RT for their users, e.g Gidi Traffic and other traffic sites, Jobsites handles also. If I'm looking for a cab driver, I find numerous especially through references on those handles. There are also groups on Facebook. I know of one designers group for graphic designers but its filled with superstars designers who will charge you N50,000 for a logo design, I won't recommend you go there. If you also have friends or relations in universities, you could find good resources there too especially for code writers who can create affordable and super clean websites for you.
One beauty with social media is that you have no right to make stupid mistakes, if you can ask questions.
Once your site is ready, you need to get the word out there and you might need a social media specialist also. The fact that you use Facebook and Twitter doesn't mean you know how to work the stage where Social media is concerned. Its always better you get someone to do that also and you monitor them. You can find them through those means highlighted above also.
Its my hope that you keep bringing your ideas to life and as you do that, may you do that with the lowest cost as much as possible.