I had the radiator in my 2002 Windsor replaced last year. I bought it from CG & J out of Alabama, my radiator was a brass/copper core but I replaced with Aluminum. The cost was $2350 + shipping $150, $2500 total.
Here is the contact information
C,G, & J Inc.
Attached is a drawing of the radiator for you to check your dimensions.
Your radiator may have been part of a design problem that Monaco had on 2001-2003 years of various models, see this bulletin
My radiator was damaged by road debris and covered under insurance. The quote you have is similar to my original quote before I found this alternative. I also had my CAC tested, it had major leaks so I had it rebuilt for $1650. I also had a new water pump and thermostat installed since they had the coolant drained. I had my system flushed and new coolant added, the put the Compleat GS in it. All this did end up costing a total of $7200 but insurance covered most of it.