It might be worth your time to look into "stepup rings". These are threaded adapters which convert a large diameter filter to a smaller diameter lens. So if you had two lenses which take filter size 58mm and 67mm, you would buy the larger size filter and a 58 to 67 stepup ring. Now one filter can be used with both lenses. Not as convenient as two separate filters but certainly less costly since you seem to be just starting out with a SLR system. Good luck.