My eyes are crossed from everyone agreeing and disagreeing.
Here are my thoughts.
I'm a contractor and this is roughly how a contract is figured.
1 identify the product or service
2 determine the number of man hours it will take to do that job.
3 review bids from contractors
3a to calculate a bid you must figure all the overhead which is the hourly cost of managers, managers benifets, your wage, your benifets, power bill, pens, pencils, computers bla bla bla. divide total dollar amount by number of man hours. all labour catagories are rated the same so as far as the contract is concerned the doorman makes $10/hour and so does the manager. (average hourly cost of all contracted employees and non productive employees

)
4 take lowest bidder
what I would do is this: since we don't have to worry about managers and junk, if you want to calculate how much electricity you use in the time you make the app, pens and pencils bla bla bla you go right ahead. as for the labour to create a webpage, if you charge:
$10/hour HTML
$20/Hour ASP, CGI, etc...
$30/hour DB admin
$15/hour maintnance
so on and so forth
the above average rate is $18.75
if you add in how much your computer costs per hour, and your pens, paper, power... you get the point it'll be a little higher.
I say, "Sir, (or ma'am) i'll do everything from HTML to your DB admin for $18.75(+plus your paper and junk) and it'll take 20 man hours so the total will be $375(+plus your... you get the idea) to do the job
A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.
- Quote by Douglas Adams