Insultingly means "in a very rude way that hurts someone's pride." It tells you how something is done, or how low or small something is, not what the thing is. A person can speak insultingly. A company can pay insultingly little. The -ly does not make the idea softer; it only turns it into a description of manner or degree. You will hear it in speech, and a little more often in careful writing ("insultingly low wages"). It is a normal word, but people use insulting itself much more.