Finn Lassen wrote:

Cheap man's way:
I'm sure you have access to an oscilloscope.

Sorry, Finn.  You killed 'cheap' as soon as you mentioned oscilloscope.

REAL Cheap man's way:

Take a piece of hacksaw blade.  One you've already worn out.  No need to go wasting a dollar on a flea market hacksaw blade.  Run it through a post on a board, so that it runs parallel to the board and is only attached on one end.

Drill and tap a 1/4" hole in a 3/4"x3/4" block of brass/aluminum/phenolic/whatever.  Cut a slot through the block so that it will slide on the blade and a bolt through the tapped hole will lock the block in place.
You can either attach the contraption to your panel, or bolt it to the top of the engine.  Dealer's choice.  Rev the engine up and adjust the block up and down on the blade.  Sliding the block changes the blades resonant frequency.  When it matches the airplane's vibration (or one of it's harmonics), it will swing back and forth.  Your looking to slide the block around to get the greatest swing on the blade.  Note how much swing that is, and stop the engine.

Hit the tip of one blade with some 120grit paper.  Not enough to go through the coating.  Just a little shave.  Run the engine up to the same RPM.  Is the blade swinging more or less?
Less?  You've got the right end of the propeller.  Hit it with the paper again, or spray a small fog of urethane/clearcoat/whatever on the other blade.  Make one end lighter or the other heavier, as long as it's balanced.   Rinse, repeat until you're satisfied.

More?  You picked the wrong prop blade.  Either put some coating back on the one you lightened, or lighten the other one.

Your dealing with extremely miniscule amounts of weight out at the prop tips to get it balance.