Mantra for abundance in Hinduism is always dedicated to one of the forms of Mother Goddess. Usually abundance is associated with Goddess Lakshmi. But Goddess Mahagauri also gives the boon of abundance to her devotees. Here is a mantra for abundance:
เคธเคฐ्เคตเคธंเคเค เคนंเคค्เคฐीเคค्เคตंเคนिเคงเคจ เคเคถ्เคตเคฐ्เคฏ เคช्เคฐเคฆाเคฏเคจीเคฎ्।
เค्เคाเคจเคฆाเคเคคुเคฐ्เคตेเคฆเคฎเคฏी,เคฎเคนाเคौเคฐीเคช्เคฐเคฃเคฎाเคฎ्เคฏเคนเคฎ्॥
เคธुเค เคถांเคคि เคฆाเคค्เคฐी,
เคงเคจ เคงाเคจ्เคฏ เคช्เคฐเคฆाเคฏเคจीเคฎ्।
Please note that the mantra should be chanted only in the morning hours after taking bath and offering puja to Mother Earth. The ideal time to chant the mantra is when the sun is rising.
The mantra should be chanted after lighting a lamp using pure cow ghee. The person chanting the mantra should sit facing east or northeast.