Which 9-Speed Cassette, chain, and should I do the rings also?

I'm switching my snow bike/beater from 8-speed to 9-speed. I don't
want to spend a lot of money on this, but hear bad things about the
nashbar & performance house brand cassettes. So, I'm going to have to
spend over $20 on the cassette. O.K.

How much more?
The Shimano M580 looks like a nice unit, but it's around $50. I'd
like to avoid spending that.
The SRAM PG-950 is mighty tempting @ $30. Then again, the PG-970
The Shimano Nexave & Deore are both $32. How do they compare to each
other & the PG-950.
Finally, the SRAM PG-970 looks good @ $40. Is it worth the extra $10
over the 950? If I get to spending $40 on this would I be notably
better off spending the $50 on the M580?*

The chain: I'd like to spend under $20. Shimano or KMC? The place
I'll be ordering from has both in stock. They don't have any SRAM
chains, and I don't want to spend over $20 on a chain for this
particular bike. Still, I hear great things about powerlinks & the
SRAM chains. Am I really missing the boat if I don't go SRAM w/ the
chain? I could buy one locally, but it'd be over 150% of my target
price.

Finally, the chainrings. This is a pawn-shop bike that until recently
was on it's original grips (though worn out) and rims (not worn out).
That's the best indicator to mileage I have. Everyone who has seen
the bike says the (original) rings & cassette look fine. I agree.
However, the chain is stretched well past spec. I'm inclined to do
the chain rings when I do the chain and cassette, but am loathe to
spend the $ if I don't need to. Thoughts?


Thanks,

Dan

*Scary sidenote: I have this same attitude when in the bike shop.
See how fast I just went from Nashbar house brand for $15 to a $50
Shimano? I don't allow myself to bring credit cards into bike shops
anymore.