HANDS DOWN Denon DL103R, available from Audiocubes @ $250. HOWEVER - I don't know what the phono is like in your preamp. Is it just a MM phono? If so - You'll need to find a step up tranny - should be able to find one and stay in budget. We're talking about a 0.3mv or so cartridge, needs a lot of gain, but worth seeking out the high gain phono.
Also - I don't know much abour your arm. the rb700... how is it different than the rb600 that I have on my P25? Anyway - if it's basically the same, you've got to find the money to upgrade the arms wiring and the stock counterweight to the michell counterweight. Also - Just as important, is the Twl Hifi Mod AKA gluing two bullet fishing weights to the sides of your tonearm bearing bolts. Makes Rega arm effective mass more appropriate for stiff Denon cartridges. Do this - and you have a SERIOUS hifi arm comparing with those in the $$$$$ No need to space vta even, armtube a little under parallel, just right for these cartridges to ROCK
Also - I don't know much abour your arm. the rb700... how is it different than the rb600 that I have on my P25? Anyway - if it's basically the same, you've got to find the money to upgrade the arms wiring and the stock counterweight to the michell counterweight. Also - Just as important, is the Twl Hifi Mod AKA gluing two bullet fishing weights to the sides of your tonearm bearing bolts. Makes Rega arm effective mass more appropriate for stiff Denon cartridges. Do this - and you have a SERIOUS hifi arm comparing with those in the $$$$$ No need to space vta even, armtube a little under parallel, just right for these cartridges to ROCK