Your Dutch Star has a Dicor
Brite Tek (TPO) roof, not EPDM rubber.
Why does it need replacing? TPO roofing typically lasts 20-30 years. Most roof problems are failed caulking (sealant) at seams or around openings.
But to answer your question, the costs vary tremendously at different dealers or shops. It's a labor intensive job and RV dealers get high labor rates. Probably $5000 is typical, but I've seen reports anywhere from $3500-$9000!.
Here is one source:
The RV Armor Process