Is $50/acre a typo?
If you are looking at Sacramento area, mapped lot in a subdivision depending on size, location, infrastructure I put at $25,000 to 100,000. or more per lot (not acre) which if a 1/10 acre lots would be about $250,000/acre ( Just a very broad example) Check out the Vineyards project in Roseville.
Another example I have a potential subdivision in the Colfax area for sale, $1.7mil for 48acres, proposed 31-35 lots. Map has not been approved, when approved could possibly be $75,000-100,000 per lot (approx 1ac lots). Of course until it sells this is all theory & dependent on what the Buyers plans are for the property.
I don't recognize those areas. For a start you can do research on Trulia or Metrolist for land for sale and parcels sold. Commercial sites like LoopNet have a lot of data too, you pay a fee for access to the data. Land price varies widely depending on location, zoning, probable use and several other factors.
Good luck with your project