Consistently investing even moderate sums can grow your portfolio with time. Bull and bear markets come and go, and along with them come short-term investment opportunities. However, investors with a long-term buy-and-hold perspective can find opportunities in any market environment. And those opportunities don't always require a lot of available cash to tap into. Even with a more modest stash of cash -- say $500 -- to invest, you can find plenty of companies to put some or all of that amount into to benefi ...