In general, aftermarket replacement parts are cheaper than OEM pieces because they use cheaper materials and/or the tolerances aren't as strict. What the usually means, is you get a product that doesn't last as long, or one that doesn't fit as well.
As far as a hood goes though, there's not a lot that can go wrong or malfunction. It may be a little thinner material than Ford used, and the panel gaps may be slightly larger, but most people would never notice.
The cheapest thing for you to do if you can be patient, is look for a hood from a ranger that's the same color as your truck. That way, you don't end up paying for a hood (aftermarket or OEM), and then paying a couple hundred bucks to have it painted too.