Myself, I've always preferred tip up and really love the Benchmade 941 / 943 series. The 940's also seem popular but I like a pointier blade.
It looks like I'll be the first one to say it, Sebenza! Chris Reeves builds his knives to be tip up. The Small Sebenza is truly one of the knife industry's great avhievements to me. For my hand and preferred carry, it's the "just right" choice for most occasions, just like Goldilocks said.
While I prefer tip up, I have in the last year or so aquired a William henry T10-CF, a Mirotech Socom Elite and most recently an Elishewitz custom that are all tip down carry. I love them all, but think that they require a flashier and more visible opening to come to battery as quickly as most of my tip up knives.
Just my opinion.
jmx
PS: Oops, missed the part about the $100.00 price limit. I originally started carrying tip up with Cold Steel Voyagers. I still think they make a good knife for the money. You could start with them to get a tip up knife in your price range. I was looking to buy a $100.00 replacement for the old CS and the search lead to the purchase of all of the above listed knives. Be Careful!