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

Too bad your thing isn’t balanced. It really limits it’s usefulness with a Pass amp

Not really as "my thing" as you so quaintly put it, is used with many Pass amps they have rca as well, and those that don’t my customers use these http://www.cardas.com/adaptors.php as Nelson said above about rca v xlr.
" Except for noise, it gives pretty much the same performance " and that noise is only becomes a factor with very long interconnects.

Nelson also made an un-named buffer for "my thing", (with over 900 world wide I think it deserves a name) the Lightspeed Attenuator to drive one or two models of his amps that are low input impedance amps around 10years ago on diyaudio, a few years later to be sold as the commercial B1 buffer by itself to be used with other passives preamps.
https://ibb.co/choBZS

Cheers George

Wrong and wrong... again. Sure, you can Drive a Pass Labs amp with single ended signals, but you get less gain, half the power, and ten times the distortion. You'd know that if you read the Su-Sy article. You'd also have known that there are definitely balanced amps out there, to, which is the ONLY way Pass amps with Su-Sy work correctly.

This is what the B1 looks like.
 https://www.passdiy.com/projects/images/content/bbp_1.png
That's not what you've got. That, and the schematic doesn't make sense. P1 isn't the volume control. It balances the voltage reference to the FETs. The volume control is obviously the LDRs that form the divider at the input. I don't understand why you keep posting that.  

Beyond all of that, Nelson didn't invent that topology. It's been used in dozens if not hundreds of input stages in amp and pre-amps for eons. You can find him saying that at Burning Amp 2015 when he discusses the nuances of that complimentary pair. 

I don’t understand why you keep posting that.

Because it was the original balanced power supply direct coupled (matched) complimentry jfet buffer that Nelson designed for the Lightspeed.
Afterwards it became (I believe the cruder) unbalanced supply re-configured capacitor coupled p channel jfet buffer (didn’t need to be matched) for the B1
Once again go away your stalking, also calling my product "thing"? you really need to see someone.

Cheers George

If you play digital, the MSB DAC can drive any amp, using passive analog volume control only. 

$1.000.000.000.00