Depends on what kind of lock you want and how heavy you consider heavy but I will make some recommendations. All these are slim and light, I didn't mention linerlocks bc I don't generally like them, less reliable more likely to fail.
LOCKBACK:
Spyderco- Police (lot of knife for size over 4in blade)
Endura/Delica=bout 4in/just under 3in excellent slim, light and well under price point.
Native=great all around knife bout 3.5 in
Calaypso Jr.=full flat ground blade, excellent knife
Manix or Chinook II=different blade, similar handle, simply awesome.
Could also check out Cold Steel's Voyager series or Boker's HK P2000 if you prefer thumbsuds, but the Spyders are better.
AXIS LOCK
Benchmade=710HS or 806D2, can't go wrong with either I'm not much on Benchmades, nothing personal, but I have to admit these are without a doubt 2 of the BEST folders on the market period.
Also the Griptillians are good for the money.
FRAME LOCK(also compression lock) all but the edc are expensive
Camillus EDC=great for the money, and CUDA Dominator=phenomenal
Strider SnG
Chris Reeve sebenza, small or large
Spyderco ATR (compression frame lock)