I used a cheap Microsoft optical mouse for a long time and could play just as well. However, it was much less comfortable and didn't even have a scroll wheel, much less a switchable smooth/notched scroll with tilt, extra side buttons, and switchable sensitivity that are standard fare on a more expensive mouse. I make extensive use of the wheel and buttons, and I don't have any hand discomfort, so it's worth it to me. YMMV, use what works and you can afford.