suggest: mysql

hi,
is it possible to use mysql instead of MS SQL?
because lots of hosting companies providing much DB space for MYSQL while only very less space for MS-SQL, to add more DB space we have to pay extra money.
if we can use mysql, will quite save money actually.

It's not implemented now. But data access layer is located at Nop.Common assembly, DAL directory (NopSolutions.NopCommerce.Common.DAL namespace).

to implement MYSQL provider, i think have to change the install script as well.

Yes. You're right.