Mssql2pgsql is a project mainly written in Python, it's free.
M$ SQL to Postgres
These are my migration scripts for MSSQL to Postgres.
Some of my prior work is not versioned, but I hope this would be useful for people under the same task.
All connections are made from a Linux box, so drivers have to be specified. I started using pymssql but it has some issues in Unicode and Blob data managment.