aspen - You seem to be missing the point here. You're using your personal experience as the basis for advice. The question isn't whether you can build a successful ecommerce site with under $5,000, it's whether an average person could do so.
The average person doesn't know oscommerce from a hole in the wall. They don't know where to buy a design template, or what to do with it when they've got it -- because they don't have Photoshop or expertise in it. They don't know a dozen high school students whole are proficient enought in photography to take quality product photos, and they know nothing about SEO. That's why they hire an expert, and that costs $$$.
This is no different than any other industry. Do you repair your own car? It could be cheaper that going to a mechanic. Do you grow your own food? It's cheaper than the Grocery Store. Did you build your own home? It would be cheaper than buying one. Do you dry clean your own clothes? Mix your own soda? Build your own cell phone? Make your own shoes?
Of course someone with the right skillset can do it all on their own -- cheaply. Most people don't have that experience, however. They have to pay for it, and as with anything else in life, you get what you pay for.
You are living proof that it can be done for under $5,000, but you're the exception, not the rule. The o.p. needs realistic answers, not "if all the stars align, and you have to know everything I know" answers.