Sorry for the late reply, I only now browse the thread again. First, I think that in general the fact that it doesn't lock isn't that crucial in the gentlemen usage scope.
There is a somewhat beefier "outdoor" version of the Compagnon, called Le Trappeur, ("The Trapper"). And that one has a back lock. Lovely but unfortunately they are around $200. I don't have one myself but they should be great and they look splendid. Bring a bit of continental style to your collection:
This Viper Gent, cheapest olive wood version should be within your budget. Italian style, great quality, liner lock:
Also consider this lovely and dependable backlocking Lion Steel Opera, also lovingly crafted in Italy, here in buffalo horn, and it also exists in olive wood. Within your budget, and a really seriously good choice:
I can also strongly recommend the
Perceval "Le Français", percisely built with a liner lock. Hyper elegant and available with different handles. Unfortunately you suffer from todays dollar/euro exchange ratio as it will cost you around $150. Truly lovely nevertheless:
http://www.couteau.com/client/cache/produit/800_____franolipli_G1_176.jpg
Finally another wonderful French one is the modern "Le Thiers" by the excellent guys from Fontenille-Pataud. Different handles, and unfortunately also around $150.