That mostly depends on when it was made, if before 1999 it doesn't qualify for any high pressure accessory barrels to include the 280 Remington, other than that, the RMEF version is just a laminated stocked 280 Handi with a medallion in the stock, it's value is what it's worth to the buyer, more if he's a collector. Since the 280 is factory available, it isn't really worth any more than the cost of the stock upgrade. Now if it was a chambering not available any more, that would make a difference, the 35 Whelen RMEF has sold here for $350 or so. A modern 280 Handi sells for about $250 new, go from there depending on when it was made.
Tim