https://adwords.google.com/select/ma...urceid=Yh91503
click through that link and get 50 bucks free advertising when you open up a new account. well, actually $45 because of the $5 activation fee.
you'll probably lose some money at first, but keep watching your stats and tweaking your campaign so you can lower the cost.
also, i would recommend buying niche keywords and excluding searches containing the word 'free.' people looking for free stuff are unlikely to buy unless you show them something really amazing.
ad copy is also really important. it's often overlooked by people who put together their account in 5mins, but write something that will make people click.