Thanks for the part number, I assumed that was the part you were after. From Schmeidmann, a repo part will probably be just under $500 landed. Wallothnesch also have them, their pricing is $199 Euro (about $350ish) plus freight, I suspect theirs will be NOS - unfortunately I don't get trade pricing from them but some prices are amazing - NOS corner indicators for a 1973 E3 3.0 were $35 each plus freight compared to $350 each second hand. So I trust both those vendors. Schmeidmann are typically cheaper for freight but parts are dearer.
Kapteijn Classic Parts is another option, though I can't vouch for them - I haven't bought anything from them yet but have been put onto them by someone restoring another E3, apparently they are quite good to deal with too.
Let me know if you want me to try get firm pricing, though I suspect that may be more than you want to spend for a race car, but if not I'm happy to order on your behalf and get it sorted for ya.