Should one total the materials, figure a shop hourly charge, guesstimate the hours to make said project, add some for overhead, add some more for profit and then add the pile up for a price?
I think not.
Car repair is figured by the hour. Ready-made replacement parts combine with specialty tools to create a repair environment which can be measured, quantified and calculated. By that measure; the cost of a couple of tubes of paint, a brush and some canvas, plus the hours (times a rate per) gives you the price for a painting or 'marble plus a chisel times an hourly rate gives you a statue'.
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If one makes the design and the work at a level of competence which the market will recognize, then we are not talking shop rates and material costs, we are talking job budgets....budget - the 'B' Word.
A serious client-consumer (often with a legion of architects, interior designers, contractors and family members in tow) will have established or agreed to a budget for the project at hand. Architects cannot specify to a client without knowing both the clients budget ("!!THAT much!??" to "Cool, when will it be done") range and the market range for the work in mind. They establish a budget.
So, when an inquiry about work lands (style and type is defined or a design is sought), the first question is "what is the budget?"
You then talk time frame: "you want it when?"
Now, with a dollar figure, a job description and a time frame (faster costs more) you can work toward a single, pre-established number and calibrate your work accordingly. More budget allows for more embellishment.
Bidding is a race to the lowest denominator, the low bidder having often lost by winning (they now have the low bid work in shop and have to produce the work for less than you wanted....pity them). Negotiating is the path to making good work (art) for a good price.
Ask for the 'B' Word next time, every time.