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, etc. 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. As a result, 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& is a dealer. It also accepts that the rifle will go out 'no longer factory original'.........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.