How much do I need to spend to get a preamp that sounds better than no preamp?

This is picking hairs and scare mongering, and just selecting a worst case scenario.

90% of amps are 33kohm input impedance or higher.

The impedance of the amps is not the issue. The impedance of a 10K control is. Per your post prior to mine:

It doesn't matter one iota where the volume control is positioned here, these figures have a perfect impedance match regardless of volume position. As do 90% of sources and amps out there when mated to ***10kohm*** passive volume controls.

*** emphasis added. With a 10K post, we can always count on the total load being less than 10K. At full volume it will be 7.5K, increasing to 10K at minimum volume in the example above.

Not to put too fine a point on it George, but your constant and false claims that active preamp manufacturers are only in it for the money is disingenuous at the very least; your remonstrations come off as hypocritical!

So how about you lay off? Others and I could have easily called you on it years ago; its become tiresome.

All preamplifiers have a sonic signature.  Even passive devices have components that in some say affect or color the sound.  Perhaps a better question to ask is which preamplifier will compliment your systems shortcomings?  This may sound strange but if I'm right that all preamplifiers have a sonic signature, some obviously more than others, then running your components, if they posses volume control is adding the least number of components to say nothing of additional cables and connectors.  I use a switching device between my line level components.  This eliminates additional active or passive components but introduces additional cable length and a switch.  I've read here that some preamplifiers enhance the sound.  This is possible for many reasons and not just the source components' shortcomings. Preamplifiers where originally designed to buffer and add additional gain but today this is rarely the need as most source components with the exception of a turntable, need additional gain for buffering. If you're not running long cable lengths then no additional components will get you closer to the source components sonic signature (this assumes that you like that signature) and in the end a preamp regardless of type will have some impact on your system.       

So how about you lay off? Others and I could have easily called you on it years ago; its become tiresome.

I think your the one that needs to lay off the false claims about passives with blanket statements about their ability to drive ect ect. Every time they are bought up, your on it to protect active preamps.
Here is a person you should kneel to as he is one who makes active preamps for a reason which I’ve outlined, yet he is man enough to tell what it is about passives that’s the real deal. You just deny them as a whole, just like the "detriments" of a certain autoformer.

NELSON PASS:
On one of his favourite premps, "which is passive" in it’s best sounding configuration.

" The Aleph L is a single ended Class A audio preamplifier combining new design thought

applied to traditional topology and the experience of twenty five years of amplifier design.
This preamplifier flows from a commitment to create the best sounding product: a simple
circuit with the most natural characteristic. The Aleph L integrates discrete Mosfet gain
devices and single ended Class A operation in a simple active/passive topology in order to
deliver the most natural sound possible. The Aleph L absolutely minimizes the number of
components in the signal path, and uses these only when necessary.
Unique to this preamp, patent pending, is a volume level control which combines the best
qualities of a passive attenuator and active gain circuitry:
At the 3 o’clock volume control position, the Aleph L offers a direct path from input to output.
The only component in the signal path is wire and switch contacts.
At positions below 3 o’clock, the volume control functions as a precision passive attenuator
using discrete resistor ladders.
Above 3 o’clock, active gain is added to the output signal in 2 decibel increments, for a
maximum of 10 dB.
As a result, you suffer the effects of active circuitry only when additional gain is necessary."

Cheers George