This is a code site so I wanted to prove this with C# and it fell apart for me.

[TestMethod]
public void TestMethod1()
{
//x = y
//Assuming y = 5.
var y = 5;

        var x = y;

        //Then x2 = xy
        Assert.AreEqual(x \* 2, x \* y); //Assert.AreEqual failed. Expected:<10>. Actual:<25>.
    }

Exactly, give him a price for the source code and developer's guide. If they don't have the knowledge or resources to develop, point them to some books, codeproject.com, and some good resources to put together a development box. Don't forget to give them a cost breakdown for you to do changes, they will probably need it.