chebby:
It depends on what you mean by 'expensive' and 'cheapest'.
Yes the traditional 'heirarchy' works well as a guide when buying all new, assuming some kind of thought has been put into matching deck/arm/phono-stage/cartridge synergy. (Especially when considering high and low mass arms and high/low compliance cartridges.)
However your Rega P3 & 2M Red could easily bear a stylus upgrade to 2M Bronze - for just less than £200 - with no ill effect. It would sound better.
Yes, ideally you would have upgraded to a Rega P5 (or similar) first but that would cost £680 plus the cost of the better stylus. It would make more of your better cartridge but at a significantly higher cost.
The same argument probably applies to something like the Rega Exact (£200). Rega presumably optimise those combinations (P2/Bias, P3-24/Elys, P5 &P7/Exact, P9/Apheta) to keep things balanced.
However, 'overstepping' the recommended combinations with say - an Exact in your P3 is not going to bring the Flat-Earth Regional Re-Education Team (FERRET) crashing through your walls for breaking the rules like they used to in the old days! You WILL hear an improvement just not quite as much.
Like all such 'rules' there is wriggle room.
I am not advocating or suggesting that someone pops a Koetsu into their Project Debut but it will not bring the heavens down if they tried a £100 cartridge instead of the £25 supplied one.
Sorry to say, cheb.........you're absolutely right
. When I souped up my Pro-ject from the standard Ortofon cartridge, the dealer, bless him, tried a couple of options, £100 + Ortofon and Goldring. I finally settled on the Clearaudio (tad more expensive).
It is strange that the difference I heard was fairly substantial. Although, whether it is better or not than the other two, as always, is down to opinions. Alternatively, I could always blame my UCS......