A little script in python:

from sys import *
from math import pi
from string import digits

def usage():
	print "Find the value of a pizza.\nUsage: pizza-value <diameter> <price>"
	exit()

try:
	radius = float(argv[1])/2
	price = argv[2]
	if price[0] not in digits:
		price = price[1:]
	price = float(price)
except:
	usage()

squnits = pi*(radius**2)
value = squnits/price

print "pizza is %.4f square units\n%.4f Galactic Credits per square unit\n%.4f square units per Galactic Credit" % (squnits, price/squnits, squnits/price)



And in a lispy fantasy language:

(with sys:* math:pi string)

(= (usage)
	(("Find the value of a pizza.\nUsage: pizza-value <diameter> <price>")
	(quit)))

(# Perl-style shortcut or for try blocks: )
(| ((= radius (/ argv:1 2))
   (= price argv:2)
   (& (in string:digits price:0) (++ price))
   (float= price)) (# function in place )
  ((usage))) (# this is the try block's except )

(= squints (* pi (expt radius 2)))
(= value (/ squints price))

("pizza is [%.4f squnits] square units\n[%.4f (/ price squnits)] Galactic Credits per square unit\n[%.4f (/ squints price)] square units per Galactic Credit")