As you listed two knives that are very different sizes, I'll sort my suggestions by size:
~$30 budget folding knife options:
Kershaw Tremor (3.75") - if you need a big, assisted flipper, hard to beat the Tremor at this price (big & heavy, though)
Ontario RAT-1 (3.5") - best option at his budget for a heavier duty folder, IMO
Spyderco Tenacious (3.375") - a bit over budget, great knife that should be considered, though
Kershaw Chill (3.125") - lightweight non-assisted flipper
Kershaw Clash (3") - bigger, chunkier, assisted flipper
CRKT Drifter (2.875") - Comes in a stainless steel frame lock version and a lighter G10 version, almost buy 2 for $30
Kershaw Cryo (2.75") - Small, tough, assisted flipper (very heavy for its size, heavy as the RAT-1)