If you want to factor in fixed costs like printer cost and maintenance, please kindly include cost of factory in china, salaries of factory workers, cost of trans-atlantic ship and crew, tractor trailer, etc.
If I buy a soap dish at the store, I don't have to buy a factory in China.
Even saying that the price of that soap dish includes a contribution to the cost of the factory is pretty naive - the factory was probably government subsidised, paid for by a loan secured on the manufacturers share value rather than their turnover, and the price of the soap dish is determined by the state of the international plastic-soap-dish-futures market.
If I 3D print a soap dish, I pretty much need a 3D printer.
If I bought the 3D printer entirely or partially for the purpose of making my own small plastic household goods and saving money, then I absolutely need to take the cost into account when calculating my 'savings'.
Also remember that the business model for home printers has, for a long time, been to sell the printer as a loss-leader and then make money on the supplies. So, really, the initial cost of the printer is likely to be built-in to the consumables cost.
I do get your argument - e.g. if you absolutely need a car to get to work every day, there's no point factoring the fixed costs into an argument about whether its cheaper to get the bus for your weekend daytrip. However, this whole thread implies that making your own goods will be a Unique Selling Point for 3D printers and that typical households will buy them to print items from pre-defined templates. Only a small proportion of users, with the creative skills and inclination to produce their own unique items for hobbies and entertainment, will have another justification for the cost.