I've scored a used roller with bearing NSK 6203-DUL1B with some bearing noise. So I pressed bearing out and pulled the seals:

Old original bearing (left) with black dusty grease; KBC replacement bearing on the right (overfilled with grease)
The original bearing contained some black grease mixed with very fine dust (source of the noise) I could not find specks for it (maximum RPM and dynamic load limits)
So far I've found 2 replacement bearings:
One is Korean made KBC

Dynamic load, lbs 2,100

Maximum Speed 12,000 rpm

Lubricant Grease (unspecified)

Temperature Range -20° to 230° F

ABEC Rating ABEC-1

And second one is SKF (Made in Argentina):

• Dynamic Load Capacity2,200 lb.
• Max. RPM24000
• Temp. Range-40 Degrees to 212 Degrees F
• Lubrication MT47 Grease
• Industry Number 6203 2RS JE
• ABEC Rating ABEC-1

Don't cry for me Argentina
This bearing has better designed seal lip which will prevent dust from getting in so I used SKF

 

What's idler roller? Is it the idler pulley bearing for the serpentine belt? If so I'm very much interested. I changed the transmission input shaft bearing with a honda bearing and I regret it a bit. It's a little noisy again. I wished I'd used a higher quality bearing than the OEM because it seems they are prone to failure.

How much is the bearing? I believe the replacement idler for serpentine from Gates is like 15$.

 

Yes this is an idler roller for the belt. The bearing is about $10 from Grainger (bough it a while ago). The seal design of original bearing was not capable of stopping the very fine dust from getting inside on the donor car; I'm expecting the same about my car as well.