It is hard sometimes to justify the purchase of lenses to people who are not interested in photography. You can buy a perfectly decent camera for a lot less than I just paid for a 77mm f1.9 Pentax portrait lens. But there will often be a better camera next year. At the present rate of progress you can expect a significantly better camera for the same price every eighteen months or so. I could for example buy a Pentax K10 today for what I paid for my ist1D last summer, and the new camera would have more megapixels (big whoop) but also an anti-shake mechanism, better controls, and a widget for preventing dust from settling on the sensor. For less money I could get the anti-shake and the dust reduction for in a K110 or whatever they are calling it, and still have the lovely light body.
On the other hand, the lens I just bought is a design ten years old. There won’t be anything better on the market in ten years’ time at any price and I doubt it will have got cheaper then either. Almost all my other SLR lenses are second hand and still great. So if you absolutely positively have to
spend invest money in camera equipment, lenses are the way to go. And this is a glorious lens for low light portraits. See my mother: