It depends on if it is possible to make precise time estimate of how long the task is expected to take for an developer with same level as your dev. It also depends on the quality of the specifications you have written. If you are unable to write clear and precise specs then hard for someone to commit to a set numbers of hours. If there are elements of research and development in the task it is also hard to set a firm price. So the answer is that it depends on the quality of your specifications and ability to describe and explain the work that needs to be done