Richard Harris , Dec 19, 2008; 11:27 a.m.
If you are looking at buying an A900, you shouldn't just be factoring in the price of the body like you say. If you want to meet the full potential of the A900's sensor then, yes, you do have to purchase expensive glass. However, a number of people have shown that you can get more than reasonable results with more "afforable" glass... Just if you splash out on the modern G/ZA glass, you are going to get better wide open performance & corner/edge performance.
The A900 has roughly the same pixel density as the A700 afterall, so it is no hard task to meet the resolution of the sensor in the center atleast. Just older/cheap glass will often need to be stopped down a lot to even out the performance across the frame.
Personally, I would have no hesitation in using 24-50/4, 50/1.4 & 70-200/4 first generation lenses on the A900 - the 50/1.4RS/SAL is excellent in my opinion, I love the bokeh, colour & size... you only need to stop it down to get razor sharp pics. But then I don't do anything particularly critical. If I wanted to really take advantage of the A900 I would be buying 16-35/2.8, 50/1.4, 85/1.4, 135/1.8, 70-400/4.5-5.6. Then I'd get two or three 500GB hard drives & I'd be good for a long time.
Spend as little or as much as you want, it's your choice afterall, no1 can tell you anything is "required" as only you know that. :)
What sort of photography do you do? What are you shooting? What lighting conditions? How large do you print?