I think it depends on several factors; the condition of the rifle (the forend problem accepted), how much SMLE's are worth in your part of the world, whether you have the ability to effect a repair to the existing forend or to source & properly fit a replacement. In the UK a tidy mechanically good SMLE is probably worth at least 700 GBP, perhaps more to the right person. I am lucky enough to have suitable woodwork to fit as a replacement, & which I have had for some time, so which does not owe me a fortune. So, to me, 400 USD equivalent in GBP would be a pretty fair price. Of course, that's looking at it from a commercial viewpoint of someone who lives in
England. It also accepts that the rifle will go out 'no longer factory new'.........something that does not bother me excessively so long as any work is done to military spec & competently. And it would reflect to a degree in the sale price.....but it would still be a worthwhile project.
Just my off the cuff thoughts......& I appreciate an individual collector/shooter somewhere else in the world might arrive at a very different conclusion.