In most cases individual crusaders had no choice in whether they went on crusade or not, because they accompanied their lord or employer. Where they did have a choice, the sources indicate that they went on crusade to fight for God - hoping for the reward of salvation in the next life and booty in this - and to seek glory and honour.
The Church did not 'con' the warriors into going on crusade. The warriors were already convinced that God approved of their fighting, and that their warrior skills were more valuable to God than the clergy's praying. The warriors took up the concept of the crusade with enthusiasm because it fitted their own ideas about what fighting was for. The warriors' belief in fighting for God is made clear in medieval epic poetry such as The Song of Roland.
By the fourteenth century the crusade had become an essential part of every noble knight's career. It was still an act of faith, but for the noble knights seeking one's own honour went hand-in-hand with seeking God's honour.
In recent years a great many translations of primary sources by crusaders about crusading have been published. Here is a brief list of primary source material by crusaders - see what you can find!
(This is taken from the reading lists I give students so it is lacking in detail. However, it should contain the vital details you will need to find things. Where I have a copy on my bookshelf, I have given an ISBN.)
Gesta Francorum trans. Rosalind Hill (probably written by a crusader on the First Crusade)
Fulcher of Chartres, A History of the Expedition to Jerusalem, ed. and trans. H. Fink
The documents in The Crusades: idea and reality ed. Louise and Jonathan Riley-Smith
Guibert of Nogent, The deeds of God through the Franks: Gesta Dei per Francos, trans. Robert Levine (Boydell Press, 1997), ISBN 0-85115-693-2 (Guibert did not go on crusade himself but he does analyse reasons why people went)
Odo of Deuil, De profectione Ludovici VII in orientem: the journey of Louis VII to the east, trans. Virginia G. Berry
The Conquest of Jerusalem, trans. Peter Edbury (Ashgate Publishing, 1996: ISBN 1-85928-291-1 hardback; there is also a paperback)
Chronicle of the Third Crusade, trans Helen Nicholson (Ashgate Publishing, 1997: ISBN 1-85928-154-0)
Ambroise, The Crusade of Richard Lionheart, trans. J. LaMonte and M. J. Herbert (1976)
Joinville and Villehardouin, Chronicles of the Crusades, trans. M. R. B. Shaw (Penguin Classics, 1963) (Joinville is a must - he's so sweet)
E. Peters, Christian Society and the Crusaders, 1198-1229 (1981).
T. A. Archer, The Crusade of Richard I (New York, 1889, reprinted 1978)
J. Brundage, The Crusades: a documentary survey (Milwaukee, 1962)
Elizabeth Hallam, ed. and trans., Chronicles of the Crusades: Eyewitness accounts of the wars between Christianity and Islam (London, 1989)
There are also useful secondary analyses by Marcus Bull, Knightly Piety and the Lay Response to the First Crusade: the Limousin and Gascony, c. 970-c. 1130 (O.U.P., 1993, ISBN 0-10-820354-3)
Jonathan Riley-Smith, The First Crusade and the Idea of Crusading (Athlone Press, London, ISBN 0-485-12094-1)
Jonathan Riley-Smith, The First Crusaders, 1095-1131 (C.U.P., 1997, ISBN 0-521-59005-1)