ORIGINAL: Nieuport nut
Glenn will print whatever size you'd like. I have a 1/4.5 DrI direct from him
If I did a 1/4 scale DrI, I'd want to go all out and that would mean essentially building a miniature flying replica vs. "a model." For example, I would consider starting with a welded stainless steel tube frame. But still I wouldn't want this to become a decades long obsession.
ORIGINAL: TFF
The last price I saw for Achim Engel's plans was $800.
I think you're right and I certainly wouldn't have paid that much. I'm not up on the bleeding edge of DrI scholarship. I just know that the Ian Stairs drawings in the datafile(s) are considered more up to date than the Nieto drawings (which I love so much). But the Stairs drawings don't provide all the information needed.
I would be interested in trying to draw up a scale structure 1/4 Dr1 plan too.
I'm just looking for sharp technical drawings that I can blow up to 1/4 scale. The lines on the crop from Stairs drawings got awfully fuzzy at 400%.