ar es1 with stock arm add rb300 or get rega p3

I have an older ar es1 turntable with stock arm and grace f9e cart.I,m wondering if i should consider adding rb 250 or rb300 ,or just move on to a new rega p3 thanks!.
what is your price range for a new front end
eltogo, a great deck...

i have just finished the said upgrade, es deck,rb-300,incognito rewire,heavyweight,vta adjuster, new rewire of motor,new pc, then mounted a new aurum beta

for the sub $500 i spent on the upgrade minus the cartridge, all i can say is WOW..... i love it(compared to a p-2 benz silver combo)
taking an older deck and giving it a new life was a pleasure both sonically and aesthetically
the sprung suspension is, imho, better then a rega "p" series
I am thinking of doing a similar upgrade to my AR turntable. How much work is this? Is the RB arms compatible with the standard AR arm?