Ortofon makes some decent moving magnet cartridges under $100. The OM-10 Super is $90 list and can be had for like $69 many places. They will fit most turntables. Grado has many cartridges under $100 (Red lists for $110; most dealers discount under $100). Also Shure and Audio Technica. Go to the link below Garage-a-records.com. They have a good selections of all these brands. I would E-Mail or call them with what turntable you use and they can help you choose one that will be easy for you to mount. That link is:
http://www.garage-a-records.com/