RE: cheap but good servos for a 500
In general, I agree with the gyro advice... I would like to say that I have four gyros at the moment... EFLRG110HL w/HS55 Servo (Blade400), Mystery w/JRDS290G(EXI450), Align GP750 w/Align DS520(TRex450pro), and last a MKS 292 (not mounted) Two crashes this year, one equipment caused, other tail touch on landing caused.
Of the four gyros, the Mystery really holds pretty good, but I am not doing anything more than flips, rolls, 180 stall turns, and 540 stall turns at the moment. It is the least expensive of all my gyros. The GP750 has a lot of tail movement.
The 500's JS5245MG cyclic servos are a done deal (I wanted all digital), so no changing that. I want a tail servo on the same quality level as the cyclic... so maybe in the $75-$100 range, and a gyro to feed it well.