€450. Not thousand. Max.
As a modified car (and that heavily) it has no chance of ever getting german historic registration, and thus would be subject to ordinary registration and taxation requirements, and since its not Euro (what are we up to now?) 7? emissions compliant that means no Green Sticker and thus no entry to urban areas ("Umweltzonen") or even sub- (yellow) or fringe-urban (red) areas (Euro 6 and 5 respectively).
Tax would depend on what the current tax rate is: when I lived there it was about 20c/cc for a then-current Euro 4 car iirc. Euro 3 would be double that. Euro 2 double *that*, Euro... you get the idea. So say tax is 50c/cc now for Euro 7 it'd be €0.5x2^8=€128... per cc
OK it can't be that bad but it won't be cheap.
Tbh €807000 in tax every year is just the right kind of ridiculous epilogue to that car's story though. You can be *that* different, but you really, REALLY, need to pay for the privilege.
Might help the national health insurance offset the cost of long term trauma therapy for every normal car enthusiast who has to endure its presence...