Fast RF digitizer requirement

I have two analog RF signals, two single simultaneous in-phase 60-MHz bursts for 15 cycles (250 ns); they are A sin(ωt) and B sin(ωt). The common mode amplitude range for A and B is 100:1. But A and B are always within 10 dB of each other. I need to get a digitized value of the ratio A/B to 12-bit accuracy LSB≈ (A-B)/(A+B) ≈ 1/8000 over the entire 100:1 amplitude swing in 1 microsecond. This has to be cheap because a large quantity has to be built.