Can you recommend a SEM/PPC keyword management tool or service?

My search marketing / PPC keyword list is growing and getting more complex to manage by hand. So I’m looking for tools that work with Google/Yahoo/MSN for managing hundreds/thousands of keywords across many ad groups. The tools I’ve look at so far are expensive, usually $500-$2000/mo and up, which is above my price range. Can you recommend reasonably-priced tools or services?
Some of the features I’m looking for include:
* keyword management across multiple engines (Google/Yahoo/MSN)
* bidding rules – i.e. increase bid (and notify me) if we fall out of #1-3 PPC position, etc.
thanks,
LC

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