One problem: He assumes that the market is being adequately served, i.e. that supply and demand are relatively equal. What if tuners have a 1 year backlog and they're charging triple what you'd pay in other cities because there aren't nearly enough of them? This one piece of information could drastically affect the accuracy of any response.

Not exactly relevant when all you're concerned with is determining whether or not someone can "estimate the answer without any specialised knowledge". But, then again, why would you only be concerned with something so trivial?