My 300E "requires" premium unleaded but I have been putting the cheap stuff in and havent noticed any knocks or pings at all. The regular unleaded around here is about 1.25 USD a gallon and premium is about 1.35 USD a gallon. Pretty reasonable but still too expensive. Anyhow I remember the day (summer of 1996 or maybe 1997) when regular unleaded was 67 cents a gallon, I wish it were still that cheap.
2003 Volkswagen Golf GL 24,000 miles. 1.9L I-4 TDI 5spd.
1986 300E. 115,000+ miles. 3.0L I-6 1st daily ride, around town only. (Gone)