WordPress plugins
A plugin built to your spec, published to wp.org if you want the channel.
Plugin development including the parts most quotes skip: settings screens, capability checks, uninstall behaviour, translations. Publication through the wordpress.org SVN repository if the plugin is meant to be a distribution channel.
StackWordPress
Project pricing
Quoted from the scope, with the estimate broken down by part.
Send the brief and get a number back.
Describe the projectDescribe the project
Tell us what you have and what should change. Within two working days you get a written calculation: the scope broken into parts with a price against each, or the questions needed to write one. No discovery call in between.