Not exactly a fan of the flieger genre myself. They are supposed to be large 45mm pieces meant to be worn over the jacket sleeve for fighter pilots to quickly tell time elapsed at a glance for navigation. Not exactly an everyday watch in my book.
With that said, I think I agree with
@AardnoldArrdvark ...forget the smaller sizes, go with the real thing in 45mm if indeed it's a flieger you want.
Iirc Five manufacturers – four German and one Swiss – supplied the B-Uhren. In Germany, A. Lange & Söhne, Wempe, Lacher & Company/Durowe (Laco), and Walter Storz (Stowa) produced the original flieger watches. Wempe and Stowa used Swiss movements; Wempe settled on the Thommen cal. 31, and Stowa used the Unitas cal. 2812. Lange used its big cal. 48 and then its cal. 48.1, and Laco used its (Durowe) cal. 5 – the only two companies to use in-house German movements.
So if it's heritage you want, go with Stowa or Laco.
However, based on your "budget concern" I'd go with San Martin if I were in your shoes. Decent quality for what you're paying and essentially the same watch, albeit a more "modern" version.
And before anyone get on the high horse claiming they wouldn't buy anything Chinese, many ETA movement parts are made in China these days so unless you go vintage, there's no guarantee that part of the watch is not from China anyway.