sure, if the job requires new software. or even old software. I mean software purchases don't pay for themselves. and its hard to 'justify' and extra $800 dollars for a one off contract to a client, where I get to keep the software.

travel costs can be a factor, work space, sub contracting. also, things i consider are the time frame the contract is to be done in. rush jobs cost more cause i have to drop the priority of other contracts to focus on the current one. long term contracts can spread the cost over time, appearing to cost less, but still covering your overhead and cost.

there are lots of factors, of course you can simplify and hopefully your coming out on top.