Lots of good recommendations here

Sounds like your friend needs something tough, and you mentioned "plant", so I'm guessing not an office job. That allows a little more leeway as far as appearance; you don't have to worry about scaring people. FWIW, all these are either in my colletion now, or I've had them in the past, I won't mention anything I don't have experience with. That said, here's what I like:
For under $200 I like ZT & Spyderco. A ZT 0566CF w/Elmax cost me $147 several years ago. A Ti Military is $190 at Knife Center.
Step up into $300-$500 and I like Hinderer XM-18 3.5", the 24 is a little big for me. They're great knives, tough, lots of options, easy to get (now), lots of parts available and you won't void the warranty if you take it apart.
I also like the Medford Praetorian Genesis T, (mid-sized version) brand new they're more but used you can find them in the $500's.
Getting into customs, the Demko AD-10+P (full Ti model) is probably my favorite, although they are spendy. I also have an AD-15+P, they can be had for a bit less. There was one on the Exchange a few weeks ago for $650.
Another one I like is Brian Tighe. I have an integral Ti Tighe Breaker that was $850 and IMHO that knife could easily go for $1,200. The flipping action on it is like no other knife I've ever handled. It's fast but smooth and controlled rather than just snappy, it's almost hydraulic if that makes sense.
A few others to receive Honorable Mention are Direware, Rassenti and Mosier.