You have an enormous SAK selection for 50 dollars. You can also get an Opinel nº8 or nº9(combined with a SAK it works great).
Buck 110 and 112 are both strong and can be found for an excelent price.
I've seen the Buck Sirus for around 50 dollars, I don't know how good it is as I haven't used it.
The Buck Alpha Folding Hunter is quite good (although bit heavy), I've used mine a lot and it stood up to the punishment well.
The Buck Rush is around 45 dollars. I like mine a lot, the assisted opening is fun, and although a bit on the small size, the blade can handle many daily cutting chores.
Benchmade Griptillians and Mini-Griptillians are a bit over 50 dollars, but they are some of the best EDC folders out there, IMO. The Pika and Mini-Pika are great buys, for only 25 bucks.
I recently bought a Gerber Gator, for 45 dollars, and I'm very pleased with it's performance. It is quite tough and the handles are very comfortable.
There are lots of good knives in the 50 dollar price range:
-SOG Flash I, Flash II, Twitch, Twitch II and Twitch XL.
-Camillus Heat.
-Lots of Case slipjoints.
-Cold Steel Pro Lite and Voyager.
-CRKT M-16, M-18 and M-21 series.
-Emerson Endeavor and Traveler.
-Gerber Firestorm, Paraframe and E-Z Out (just $22!).
-Kershaw Chive (the Blur is a bit over 50 bucks, but completely worth it).
-Ka-Bar Dozier folders, some of the best "bang for your buck" knives in the market.
-A.G. Russell's one hand opening knife.
There are a lot more I'm forgetting, for sure.
Do a search by price range on any of the on-line retailers and you'll be amazed by the number of good knives available at that price.
Of course, you still need a Sebenza.