I always have difficulty convincing clients to spend money on logos but good ones do take skill and time to produce and then have to be developed into a consistent visual style across a huge range of items and merchandise.
Many years ago on hearing me whinge about this a client of mine said that he had to sell snails in garlic and I should count myself lucky. I'm not so sure. More than two decades on his restaurant is still using the logo I designed so I reckon it was good value.
One of my current favourite design books is Meta Skills by Mart Neumeier.
Here's a link http://www.amazon.co.uk/Metaskills-Five-Talents-Robotic-Age/dp/0321898672
Here's what Marty says about what a logo is worth
"A logo is not a brand. But is it valuable? Probably more than most companies realize. A logo (let's call it a combination of a name and graphic treatment) has the ability to compress the purpose, personality, and uniqueness of a brand into an elegant, meaningful symbol. This symbol, if conceived well, can be unpacked by customers in ways that are hugely valuable to the company over many years.
How much should the company pay for a logo? About as much as a car, as it turns out. Think about the logo as a company car for brand meaning. You can buy a car for $500. It may be an eyesore, but it'll get you from A to B if you're lucky.
At the other end of the spectrum, you could pay up to $500,000 for a uniquely designed beauty with impeccable engineering. It'll strike awe into the hearts of onlookers, and perform well for a good 25 years or more. Realistically, however, the right symbol for most companies will be in the S20,000 to $75,000 range, depending on their prospects. Is your brand symbol worth the price of a car? What kind?"