What's next after my 300B Rega Turntable

Give the Audio Advancement Eurolab a spin for 30 days with a money back guarantee.I put the Schroeder Model 1 on mine.I have heard good things about the Golden Gate arm and Schroeder Model 2.These combos should fit within your price range {973} -875-8705 Hart. Happy hunting!

Teres Model 255 Signature in Cocobolo. Origin Live Encounter tonearm, Shelter 501 MkII cartridge. That gives you the whole package for just under $5k. I speculate that you would have a very difficult time beating that for $10k, or even more.

Origin Live Resolution table. Origin Live Encounter tonearm. Shelter 501 MkII cartridge. Total is just under $4700. Origin Live gives a 14 day money back guarantee (I think you pay for shipping, though). They have U.S. dealers listed on their website.

Wait a minute. We have a question here about which of the "Poobahs" is higher. Is it the Great Poobah, or the Grand Poobah? Is anyone "pulling rank" here? Is there some kind of accepted "Poobah" hierarchy?

Didn't mention the cart you have. Why do you want to dump the rega so fast?
Since you say you're "new" to vinyl (welcome!)I'd keep the rega w/ unknown cart, and put $3k into used and new vinyl, save the rest, and wait till next year.

Do not ever talk to dealers about recomendations. They will always have one. It will not be what you have, nor will it be for free.