Agree with Raul, he hit the nail on the head.
Aiming for some cost ratio is largely pointless, since the performance and compatibility of components cannot be judged just from their cost. OTOH, good lessons can be learned by looking at the ratios of systems that work vs. systems that don't. In that vein, here's my system with either of two carts:
Cart 1 (LOMC).....4
Cart 2 (MM).........0.1
This favors the phono stage, TT and arm over the cartridge more than NickT's list, extremely so in the case of the MM (thanks, Raul!).
The sound with either cart is phenomenal. You'd expect that from the $4,000 LOMC and it's certainly the better of the two, but the real lesson is how great that little MM sounds. No one would guess they were listening to a $100 cartridge in a $20,000 front end. This crazy cost ratio (top class components, throwaway cartridge) works remarkably well.
OTOH, every time I plug my world class LOMC into a system with a lower quality tonearm, turntable or phono stage the results range from boring to terrible. Very revealing cartridges reveal system weaknesses just as well as they reveal music. Do not make this mistake.
Get your other components above the level of your cartridge or you'll never hear what it can do.