For DIY, you can 3D print the filter adapter on Shapeway and assemble it yourself for minimal cost.
Part 1 of 3 is this part which you can 3D print on Shapway, then you need to glue it to the other 2 parts below to complete the assembly yourself.
Part 2 of 3 is the slip-on case for the iPhone 5s you can purchase from many online stores. Alternatively, select the "universal" 3D model and use it with a clip-on mount.
Part 3 of 3 is the Thorlabs part.