OP, you're skipping the $320 in extra pic bridge you need to make the NV setup operational ($170 front rail +$150 tall action rail). No Cap the bag rider is also nominaly, $85-100 MSRP. Call that ∆$400ish, on top of your $538 estmate, for a total ∆ of ±$950 (rounding slightly).
If you look at it thisway the v4 upgrade is almost free, at only ± $300+ some change. AND...If you really wanted to into #girlmath...you could say the V4 upgrade "is completly free", since the ∆ $300 is just a cost-of-living adjustment of 5% vs the last price hike.