First of all you don’t have to be ashamed of doing what is right even when in the eyes of others wrongdoing is accepted.
In the Succos issue of Hamodia, a man writes how he walks the street without his glasses to avoid looking at women not dressed in the realm of tznius. He ends stating that he is in the process of converting. Try to get hold of the paper and read it in full.
There are gemachs that collect only clothing in good condition and give it for free. Perhaps you could avail yourself from some of these.
The same issue of Hamodia wrote about the problem of tznius at the Kosel and at the same time the same people who come dressed improperly at the kosel would dare not go improperly dressed to places of worship of other religions.
Kol Hakavod for doing what is right. You don’t have to defend yourself to your loved ones just try to explain yourself that you are following the ways of the Torah and the uniform of Torah is tznius in all matters, including dress, speech and behavior.
If you really are honest of not being able to afford more skirts, let me know how to get in touch with you and i will be more than glad to help you purchase some more clothing that are appropriate.