Wheel weights are going to be about the most expensive form of ballast. Around $1 per pound. AND...they acutally provide the least effectiveness pound for pound vs a counterweight. (this is assuming you are wanting more weight due to FEL use).
Basically, 500lbs on the 3PH does MUCH more than 500lbs of wheel weights. Since 500lbs on the 3PH is BEHIND the axle, it is actually a counterweight, and takes weight OFF the front axle. Whereas 500lbs on the rear axle dont do that.
And without sufficent counterweight, you put a huge strain on the front axle. For example, without wheel weights, you can be able to lift the rear tires into the air. That puts the ENTIRE weight of the tractor, loader, AND load in the loader ALL on the front axle.
Now lets say you add 300lbs of weight to each tire, and you can lift more in the FEL, but the loader still has enough force to lift the rear tires, now you just added another 600lbs to the front axle PLUS the addition load the FEL can lift as a result.
Personally, I would opt for a heavy implement or make a counter weight with a barrel and concrete. MUCH more effective, and MUCH cheaper.
Ofcourse, if you are asking because of things like plowing or disking, just ignore all of that.