価: value - but not an actual dollar amount (that'd be 値段) . 価 is value as in, ('the value of the antique goes up with time' or 'I'll estimate the value, using my jewler's loupe and tweezers.')

 値: value in a math or science sense. Numerical value.

 物価:ぶっか: price of a commodity as a whole (gas prices are up! Tokyo prices are higher than in the countryside!)

 値段:ねだん: price of one item. Also, value of a thing (this plan is useless! She places a high value on honesty)