The 555s are great cans and superb value at their list of around $150. At $80 they would be a positive steal. Don't even think about 600s or 650s for use with a portable player or PC, the sound would suck. Those puppies need a proper headphone driver stage to perform, without it they sound lifeless and awful. The 555s would also benefit greatly from a headphone amp meaning you have a great step-up in quality to look forward to when funds permit.

Good luck!