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:
सर्वसंकट हंत्रीत्वंहिधन ऐश्वर्य प्रदायनीम्।
ज्ञानदाचतुर्वेदमयी,महागौरीप्रणमाम्यहम्॥
सुख शांति दात्री,
धन धान्य प्रदायनीम्।
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.