$150 is too much, unless you're in San Francisco or some place with elevated prices and a mixte-happy populace.

The advantages of a Nishiki, Shogun, Centurion, etc mixte is that they are not French. They use normal parts.
That's worth about $25-$50 in lack of aggravation, but doesn't make the bike worth $150.

Around here, $40-$60 for a Peugeot mixte, and $25-$50 more for a Japanese model, pre-overhaul.

After overhaul, the single speed mixtes go to hipster girlfriends for about $150-$200 depending on the wealth of the hipster. A powder-coated one that looks like new can go higher near campus; it's all about image.

Geared mixtes here with upright bars can go $200-$250, but I doubt there's much profit involved because it's a lot of work and fuss to get them just right. Labor can easily come out to about $2/hour by the time you find what you need, put it on, etc.

The hardest thing to find in many cases is the bottom-pull rear caliper.