Is it permissible to reject a religious and well-mannered suitor because of his stinginess, knowing that he is financially comfortable and the fiancée's financial circumstances are difficult?

Stinginess is a reprehensible characteristic, and "What disease is worse than stinginess?" What you have mentioned is not enough to describe the suitor as stingy, for he might not be aware of the prevailing custom. Judging a person as stingy requires multiple instances. You can, through your guardian, inquire about him and be frank with him. If it becomes clear that he is not stingy and possesses good character and religious commitment, then we advise you to accept him. However, if it appears that he is stingy, then our advice to you is to break off the engagement, because stinginess is one of the worst diseases, and scholars have warned against associating with a stingy person. Ahmad ibn Hanbal and Yahya ibn Ma'in both agreed that they do not know of a righteous man who is stingy. Bishr ibn al-Harith said, "Do not marry a stingy person and do not deal with him." Ibn Abd al-Barr described stinginess as "a chronic disease that blemishes chivalry."