>>212889222
Volksarmee raincoats without rank shoulderboards are cheap. Still LARPy but most wouldn't recognise it as military. Volkspolizei raincoats are a slightly different design but could work too.

You can also find Kampfgruppen jackets without the red flag patches also. Just know they're not super high-quality but they are cheap. They also have winter variants with insulation padding which are alright, little rarer.