I assume you are talking about Remington Order #4449 that comes with the Wilson Combat Ghost Ring rear sight and XS front sight post?
If so, that is the model I want to get too and I haven't found anybody selling it much cheaper then the price you quoted. IMHO, no $150 is not too much to pay for a Synthetic stock set and those sights. Turn it around, check around and see how much it will cost you to replace the stock set and have those sights installed and then add that to the $399 for the base model.
In all likelihood, you will find it comes out to be more then $550 and the sight install may not even be done as well as the factory job.
Just my $.02