>>It seems to me the prices on used DW's has doubled in the past 4-5 years<<
Until it comes time to sell one...then expect to take a bath. (with a very few exceptions)
I put a 15-2 in 90% condition with a 2.5", 4" and 6" barrel on my local gun forum this summer and it sold in days for $500. Maybe I just got lucky. Gunbroker shows sales of single barreled 15-2's at $350 and $125 ea for barrels. Nothing cheap anymore.