Some of the best long work-distance objective lenses I have used come from Mitutoyo. They are definitely not cheap, but compared to Zeiss, Leica and Nikon, they are actually quite reasonable and affordable. You may, however, need to set up your own imaging system which I am personally not averse to when the need arises.
Not knowing exactly your requirements other than 50X and WD > 10 mm, it is difficult to recommend exactly which one. You can find them here:
Dmitry, mitutoyo's MPlan Apo 50x code#378-805-3 specifies NA=0.55, WD=13mm, f=4mm, res=0.5 mlcron in radius. I think price is higher than 1k💲. http://www.mitutoyo.co.jp/support/service/catalog/03_kogaku/14020.pdf#page=18