property :price, Float, :required => true, :format => /$?d{0,3}.{1}d{2}/

b.price = params[:price]

property :price, Float, :required => true
validates_format_of :price, :with => /$?d{0,3}(.{1}d{2})?/

c = params[:price]
c[0] == "$" ? b.price = c[1,7] : b.price = c