If it's a stockman, the Buck 703 is excellent. Another good one is the Camillus #67 stockman.
A Swiss Army knife might be good, but for heavy-duty cutting around a farm, I think a stockman model would have knife blades that are more durable.
Also keep in mind, depending on how hard he works his knives, very few knives, even top-quality knives, will last a full lifetime of VERY HARD use, like on a farm. But will probably last about 10 to 20 years of tough daily use.
There are a lot of great choices out there for well under $50. Besides the aforementioned Buck and Camillus, also Schrade (their Uncle Henry line has the rust-resistant blades), Case, Queen, etc.
Jim