Aye, Park Place here by Arlington quoted me $16.80 for a master square head key for my 1989 300e.

Whatever you do, just do not have a brass key made, reading from people's posts here, the brass damages your tumblers.

__________________
2006 BMW M5 "Heidi" @ 109,000 miles
2005 MBZ C55 AMG "Lorelai" @ 165,000 miles
1991 MBZ 300E "Benzachino II" @ 165,000 miles
1990 MBZ 500SL "Shoshanna" @ 118,000 miles

(On the hunt for a good used M103 engine as of 6/10/23, PM me if you have one to sell!)