I'm very far from up with the latest and greatest in car audio, but what I would do for any car I was giving an audio upgrade is:
1) Decent speakers - not necessarily OEM, but I guess at up to $50 per speaker, and for something that fits the original holes.
2) Consider replacing wiring from head unit to speakers - unless convinced that what's there has good conductivity, little interference and no physical damage - up to $50 for new wiring I guess.
3) Head unit - no ipod connectivity, just USB and of course CD. [Disclaimer: I have a bit of a thing against ipods]. $200 max, due to theft risk and impending obselesence (digital radio). In that price bracket, the best quality audio comes from CD, especially when coupled with hydro-pneumatic suspension
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4) If really getting serious, consider some sound-proofing work on the car
I'd be unwilling to spend any more than this ~$400 total - if anything, spend the $ on the "infrastructure" (speakers and wiring) rather than the head unit.
No need for an amp. Keep in mind too that you should still be able to hear the sirens from emergency vehicles over the top of your music - 116es may be built strong, but fire trucks are stronger.
Sorry to still not answer the original question posed - it's more of a "what would be out there if I had actually done it."
Lukas