What are the most balanced relatively neutral cartridges at each price level ?

best in the $5k and way up IMO is the air tight opus 1 and others in the line, they are superb

Agree with @jperry - Ortofon, other than the SPUs

Huge fan of the PM series by Nagaoka. 

level 1 - up to$1k. Ortofon MC Quintet Black

level 2 - up to $3. Ortofon MC Cadenza Black

level 3 - up to $5k. Ortofon MC 90x or for a few dollars more MC Windfeld Ti

level 4. - any price. Ortofon MC Diamond

At best, you will get different responder's preference at each price level, and not necessarily a preference based on your undefined terms.  I will contribute some of my favorites at or near level 4:

Audio Technica AT ART1000 (recently discontinued at $4950)

Audio Technica AT ART1000X (new model I have not yet heard at $5,500)