I don't mean to be flippant, because this is an interesting question, but I would say that considering we can't even come up with solid numbers of participants in a Crusade, attempting to categorize their motivations would be futile.

However, I can tell you that at least some of them were. If you focus on the First Crusade and its leadership, you have men on an a range of motivations, from Bohemund of Taranto, whose motivations seem, in retrospect, entirely mercenary (especially considering his behavior at Antioch). Close to him would be Raymond of Toulouse, who was already rich and powerful in his own right but sought further gains for himself in the Levant. At the other end of the spectrum, there are men like Robert of Normandy, who mortgaged his entire Duchy to his brother (the King of England) to fight the Crusade and who promptly returned home after its conclusion.

As for the soldiers and commoners, I would say that they weighed heavily towards faith as a motivation. Consider the People's Crusade, which, while foolhardy and ultimately deadly to most involved, was very clearly an outpouring of religious fervor. For the Crusade itself you can look at how the army responded to the miracle of the Holy Lance in Antioch - they were inspired to fight and break the siege thanks to a religious symbol.