If you are thinking SME IV, the Rega RB 300 will be as good as, there are many tonearms today that are only in the Market as Rega had no Patent.
As a result of Rega success in the market back yonder, Brands being hurt come onto the Market with New Models as plagiarised Rega Design and Geometry.
SME and others fall into this practice.
A RB 300 can be acquired for approx' $300, as a model it can be modified at very reasonable cost. Patience might even get a modified version for the monies wanted to be outlaid.
As a Tonearm user, I moved on from fine tuned SME 3009's to the SME IV, during this period of using the IV, I also used a TA Design based on the Rega, a Audiomods Series Five Micrometer. The IV and Series Five were almost indistinguishable in use.
I has a similar experience when selecting the IV as a purchase, even though not experienced on the home system, a IV and V were not able to distinguished into a category where one was noticeably a improved performance over the other, hence I bought the IV.
A modified Rega, should not be too far off in performance to any of the above mentioned TA's, maybe ? it would be a parity performance at a very fair cost with a lesser attractive aesthetic.