Where can I buy residential land at a cheaper price in Mauritius?

Isn't that the million dollar question?

You have 2 options:

1. Buy directly from the owner so that you avoid "courtier" fees. Agencies will push up the price of houses as well because they get a percentage as commission, so the more expensive they can sell it for, the more profit they make.
2. Ever heard of property auctions? These are houses/land which have been seized for a number of reasons including non-payment of debt or non-agreement between heir and the property goes to sale by auction. You need to know the process extremely well if that's something you'd like to do as bidding in court is contractual and more experienced bidders may know market prices better than you.

Both options require extensive research and dedication but you'll definitely get prices below market value if you go with these.

Good luck!