You can hire me on a per-hour basis (adhoc), or for an entire project.
Adhoc work will be logged while I work on your project and I will invoice you at the end of every month.
Project-based work is a much better approach if you want to fix your costs. After understanding the scope of the work I will give you a set price to complete your project; it includes a complete app design, hand-off to a developer, and QA after the developer has finished the coding.
Please contact me if you would like to discuss a project.