Holmburgers, this isn't the best site for information on LF gear. The US LF site http://www.largeformatphotography.info/forum/ is better. So, if you read French, is the French LF site http://www.galerie-photo.info/forum/

Look for f/6.8 Leitmeyr Weitwinkel lenses. 90s and 105s aren't that rare on eBay. They're not highly regarded, are relatively inexpensive. I have a 105, it is a 4/4 double Gauss type like the 90/6.8 Raptar/Optar (might be in your price range), the very highly regarded 100/6.3 Wide Field Ektar (probably out of your price range, but not always), and the 100/6.3 (also f/9) Meyer Aristostigmat. Beware of lenses in barrel, some of these things won't go directly into standard shutters and even standard shutters aren't as inexpensive as one would like. Prime example, my 100/6.3 Aristostigmat in barrel.

If you want good image quality on the corners no 127 mm Tessar type will suit you. That includes Rainphot's prized 127 Ysarex.

There are two coverage concepts floating around. "Puts light in the corners," "puts good image in the corners." Impossible to know which anyone uses without asking.