If your data size is 250MB then unless you can compress that (and it may be possible you'd have to experiment with SQL Compact Compacting (
Maintaining Databases (SQL Server Compact)[
^]), ZIP, and suchlike you aren;t going to get any appreciable reductyion in size.
To be honest, unless there is a lot of redundant info in your DB, a reduction of over 50% in size is very unlikely - it will depend hugely on what your data is and what type of data you store it as.