Is it permissible for a son to disobey his parents after they refuse to let him marry another woman with a lower dowry, and force him to marry the one they chose for him with a dowry he cannot afford, while he fears falling into sins?

It is not permissible for parents to compel their child to marry someone they do not desire, and their child's disobedience in this matter is not considered an act of defiance (disobedience to parents). If, in addition to this, the dowry is high and there is fear of temptation, then it becomes obligatory to proceed with marriage without regard for the parents' opposition, while ensuring to respond to them courteously and to appease them later. The validity of the marriage does not depend on the parents' knowledge or consent.