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

Less than 2k. Try “AM Audio”, state of art building, perfect matching and quality selected components, no capacitors into sound routing, dual mono, dual power supply, quality strong metal construction, gold-plated pcb... just volume and input

scope of preamplifier is not to sound but to adjust impedance and normalize gain, bringing the signal, as it is, from source to the amplifier.. for this reason couldn’t be passive and has not “to sound”but just to bring the sound as a diligent steward.. 

it should be enough expensive to ensure building at top quality rating but not so expensive more than a good source or amplifier, if not we are going to revert the sense of things... 

You’ve lost it kosst, go and down another bottle. Go back to complaining about fins on the sides of chassis, you were almost believable then. 

George, I need two inputs because I listen to vinyl too.