You might want to post this down on Harley's forum. Collectors there make one heckuva resource, and if Harley doesn't know about a firearm, it is truly rare.
Had one a few years ago just to play with--i'm not aware of any great amount of interest in 11-48s by collectors unless it's some fancy target gun or something. My guess is that it is just a good shooter and probably worth less or maybe same as used 1100....Just my 2 cents ....Dick
Wedge:
Not much on the Rem 11-48:
It is pretty much the same gun as the Rem 48A except the gauge and has a 3 shell mag. It was discontinued in 1969 and the value is not listed in my newer mags, and the value listed is from an older book about $200.00.