Here are three good ones, which are available at low cost on ebay.

The buck mayo northshore (BU-173)
http://www.knivesplus.com/buck-northshore-knife-bu-173.html
a solid liner lock with pocket clip for tip down carry, and only weighs 2 and a half ounces.

the buck mayo cutback
http://www.oregonknifeshop.com/buck-mayo-cutback-knife-174.html
a frame lock, pocket clip with tip down carry and weighs 3.3 oz. This knife often sells on ebay for under $20 and it's a bargain.

I've used both of the above extensivly hiking & camping as my main knife.

Boker trance.
just got one and i love it - although i haven't useed it yet! Mainly because it perfectly fits my hand. Framelock with tip up or down carry options. Mine is non-serrated, but it also comes in a combo edge if that's what you want. Weighs 3.1 oz. Blade is 2 & 3/4 inches long, while the two bucks are just over 3 inches.

The buck mayo hilo is a bigger version of the cutback; over a 3 and a half inch blade.

All of the above should fit your specs without a big outlay.