Hello,
You need turn off PayPal and then you can add any value (in your case MXN PESOS) in Currency field.
(RealEstateManager : Settings - Administrator Settings - Price Options - Currency - editCurrency )
For turn off PayPal: RealEstateManager :: Settings - Pay - Show buy for booking: NO
and Show buy for sale: NO
If you need add MXN PESOS in Paypal, install last version of RealEstateManager and use value, which use Paypal for MXN PESOS.
More deatils:
developer.paypal.com/docs/classic/api/currency_codes/ - this code need put in field of Real Estate.
Sincerely Yours
Taras
OrdaSoft team