Praise be to Allah.
My dear brother, I appreciate your confidence in me and I ask Allaah to make us and you strong and steadfast, and to guide us. With regard to your question, I offer the following comments:
1 – The problem you have is not with regard to marrying a second wife, or divorcing your wife. The problem, as you mention, is a financial problem. So long as you are not able to marry another wife, then you should keep the wife with whom Allaah has blessed you.
2 – Whenever you are able and have the financial means, and praise be to Allaah that He has permitted plural marriage to you… In my opinion that is easier for a woman to bear than divorce, especially since you have children from her.
3 – Try to look at the matter from a different angle. You may find many positive things in her, and beauty is not everything, believe me. How she behaves and treats you… and many things which are ultimately more important than appearance. For with time you will get used to her appearance, and how she behaves will be what matters…
4 – Imagine that you find a very beautiful woman and marry her… then she starts to treat you in an arrogant or impolite manner… or she treats you and your family badly… what would you do?!
5 – You should be objective and not burden yourself with more than you can bear. Look at the matter from different aspects. “it may be that you dislike a thing and Allaah brings through it a great deal of good” [al-Nisa’ 4:19 – interpretation of the meaning]. And remember the advice of the Prophet (peace and blessings of Allaah be upon him): “Look for one [a wife] who is religiously committed, may your hands be rubbed with dust [i.e., may you prosper]!”
May Allaah help you, protect you and make you steadfast in following the path of goodness and truth.