You can get a set of suspension techniques springs for $167 that IMO are perfect (height and street damping). You can go lower but not without rolling the wheel wells or other mods.
click here for picture of my car with st springs
http://www.bmw2002faq.com/component/option,com_forum/Itemid,50/page,download/id,51871
here is where i bought them
http://www.autopartsdealer.com/suspension_techniques_suspension_components-p403603-p.html?utm_source=froogle&utm_medium=cse&utm_campaign=froogle&utm_content=APD403603