For pondicherry i believe within 4k-5k is enough
and for mahabalipuram it's a one day trip so within 1500 rs you can do a round trip. try this 1st day visit mahabalipuram on a rented bike or scooty to mahabalipuram and in the evening around 4pm or 5 pm leave from mahabalipuram to pondicherry as this will on OMR ( old mahabalipuram road) road and you have to come to ECR ( east coast road ) road. try to stay near auroville near by time travellers hostel and visit maitri mandir or auroville early morning.
if you want to go inside then you have to book one day advance to meditate inside which is payable like 50-100.
next day try to visit pondicherry city which is 8-10 kms away from auroville and visit th beach and stay nearby in Airbnb in dormitory or good hotel and enjoy the rest views ... TIA