A lot of the time when clients cannot afford SQL 2005 standard, SharePoint usually gets installed as a single server farm with an Windows Internal Database. The windows internal database is actually a version of SQL 2005 Express edition. It is actually preferable to use this internal database over a copy of SQL 2005 Express edition because you are not limited to 4gb with the internal database, as you would be if you used an external SQL 2005 Express instance.
Always keep in mind that you can connect to the Internal database using SQL Management studio express found here:
When you download this you can connect to windows internal database by using the following server name:
This will enable you to see the databases used inside the windows internal database. This is exactly the same as if you were using a standard version of SQL.