Assuming the r2 is the R squared from an OLS regression, for a linear model, the coefficient of correlation between price and SINAD is calculated from the slope by multiplying by the standard deviation of the SINAD and dividing by standard deviation of price. The R2 measures how much variation is explained by the model price = a*SINAD + b.
If you want to determine how much more one should expect to need to pay to gain 1 dB of SINAD, you can just read of the slope. If instead you want to determine how much greater SINAD one can expect for a price increase of one, price and SINAD should change places in the model (the slope then being the reciprocal of the other arrangement).