Of the four you mention, there's a soft spot in my heart for the Buck 110. Wonderful knife, tough as nails and will last you a life time. My oldest 110 is from 1972 (my grandfather gave it to me in the late 80s) and it's just as tightly put together and sharp as my 2005 110s.
$30 will get you a standard 110 with 420HC steel (people will bash the steel from time to time, but Buck does it right and it'll take a razor edge and touches up easily). Around $60 will get you a Cabela's Alaskan Guide 110 in S30V or the relatively new Bass Pro 110 in CPM154 (I've got the Cabela's version, wonderful knife). Between $80 and $150 will get you something from Buck's custom shop with your choice of blade steel, handle material and bolster material.
Overall, it's my all time favorite folder, but it's big and it's heavy. If you don't like belt carrying a folder, the 110 isn't for you.
Does G10 count in your "no plastic" policy? If not, and if you can find one, look for an old Kershaw Hawk. They were discontinued around 2000 but pop up from time to time for reasonable prices. I have the Japanese made G10, ATS-55 version, but there's also an American made version with titanium scales. It's a liner lock, but it's a good liner lock. I think I got mine for around $35 a few years back.
Don't count out Spyderco either, they use a lot of FRN handles but they're good knives and they don't feel cheap. I just got a Centofante 4 that I'm falling in love with for every day cutting tasks. It's not a heavy duty knife, but it's beautiful (not just by Spyderco standards, it's a good looking knife) and that wharncliffe blade will cut anything. Cost right under $50.
My EDC for the last year and a half has been a 154cm Benchmade 710. It's at the upper end of your price and size range, but worth looking at. It's a big knife, around the same size as the Buck 110, but about half the weight. The 710 carries like a small knife and doesn't get in the way of anything else in the pocket that it's clipped to (I keep my phone in the same pocket and never have trouble getting it out). Cost was under $110, but look into your knife laws when considering an Axis locking Benchmade as they can be considered gravity knives in some jurisdictions.
Good luck and have fun with your search. Unless you're smart and find the knife you want and never return to this site again you'll end up with more knives than you intended to have.
