Short answer
Income is an important practical consideration, but it should not be the only or main measure of a person's suitability for marriage.
Islamic Guidance
What Islam teaches
Islam places importance on religion, character, responsibility and good conduct. Financial ability matters because marriage involves responsibilities, but wealth or income alone does not determine a person's worth or suitability.
Practical Guidance
What you can consider
Consider income together with character, financial responsibility, lifestyle, expectations and the person's ability to fulfil marital responsibilities. Avoid treating a salary figure as a complete measure of suitability.
Sources
Qur'an 49:13; Sahih al-Bukhari; Sahih Muslim.