licensing question for a UAT env.

Hi,

what version of SQL Server can I use for a UAT environemnt?

the solution to test has sharepoint foundation + 3 SQL Server servers (SQL, OLAP and SSRS on 3 servers).

the UAT will be done by 50users.

does an MSDN license is enough? or 3 DEV edition of SQL can be used?

or do we have to pay for the enterprise edition (which is what the prod will use)?

thanks.