New tonearm

ytou might consider the cartridge first, before changing arms.

There is a rewire kit from INCOGNITO for the Rega Arm available. It is huge step up compared to stock.

You'll have a hard time upstaging the Rega arm for 1k. Put your money elsewhere; lots of options, such as Jaybo's.

Finding a drop-in tone arm under 1K to beat a modified Rega? Easy.

Bluenote Borghese, Bluenote B5 and U3 signature, Graham Robin, Origin live silver, VPI JMV 9 and a host of other that I cannot think of now. Any of these will outperform a RB and then some ...

If you are willing to go used, you’ll find a lot more.

Note, make sure that the tonearm you select has the correct mass to match with your cartridge compliance.

Regards
Paul