Prototyping without development boards sometimes may seem impossible. Always before starting producing real design there is always prototyping part of work. Sometimes there is more convenient to use breadboards. But if you know that you will need to prototype more devices based on same microcontroller, so it is better to develop universal board which is more stable and easy to use than breadboard.
For USB prototyping PIC18F2550 is a good choice as it has USB port built in and no additional circuitry is needed. The PIC18F2550 is a USB2.0 Full Speed Device(12Mbit/s). Sadly microcontroller doesn’t have bootloader built in, but you can always use third party USB bootloader like Sprut USB bootlaoder. Board schematics and PCB is available for download in eagle format.