Comparing the specs for a new custom PC to the fixing of something is totally different.
You can quote for fixing something by just saying "I have worked out it will cost me X to fix", where speccing up a PC you have to send them the specs of it, otherwise they are going to be asking "Why does it cost that much, what does it come with? Blah blah blah.
Actually, in many cases, it's rather the other way round. It's pretty easy to spec up, and price up, a new PC. all you really need to know is what it's to he used for, and preferably, the approximate budget of the customer. Then you can spec the best hardware for that purpose, price no object, or the best for the specified purpose within the stated budget. But "fixing something" requires determining what's wrong with it in the first place. Until you start taking things apart, or down, it can be hard to be sure what's involved in fixing it.
An awful lot depends on the "project", which could be anything from replacing a washer on a dripping tap, to building a home extension, to building a bridge or a 60-storey skyscraper. On the washer replacement, I'd expect a pretty accurate estimate of time and cost from any half-competent plumber, after a one minute examination, or even over the phone. Good luck getting a fixed price quote for a 60-storey skyscraper.
However, if building a home extension, there are a number of ways of bidding for that kind of job, but a "quote" requires a careful assessment of work involved, potential risks like groundworks problems, materials required (which will depend on customers exact expectations), and as it's a fixed price, requires quite a margin of error to cope with the unforeseen. The more careful the examination pre-quote, the more time it takes but the more you can narrow down and/or eliminate risk, so the lower the risk padding element can be and the more apoealing, overall, the quote will be.
Clearly, OPs situation was more at the dripping tap end of that spectrum, and charging for that consult/quote was cheeky unless agreed in advance. But it all depends on the type of work being down, and the extent of it, because the risk element goes up exponentially as job size increases.
If the customer wants a quote, rather than a more open-ended time and materials bid, he is either going to be paying a large risk premium in a fixed-price quote, or there's going to be potentially extensive work involved prior to quoting, which takes time and, personally, I'm not doing unless it's paid-for.