I think the RT-S in 20's is new. I have not heard of any with those wheels on this forum or others. They sure look good though...I'd like to see them mounted as well on a challenger.
Weld shows sizes for the 20" rims on their website but no prices. Found a dealer and price for a 20x9 is $750 a wheel. I just bought 17" RT-S wheels and they ran around $480 a wheel.
The RT-S wheels are not manufactued by Dodge but are made by Weld Racing Wheels. They come in 17",18" and 20" to fit our cars. I'm running 17" on my car for that "Old School Muscle Car Look".