How to calculate resistor values for certain filters?
The two parts of the filter interact to some degree depending on the values. If you added an op-amp buffer between the two halves they would not interact. But the interaction is probably not important here.  

Since the high pass filter is to block DC typically the impedance of C1:

\$X_{C_1} &lt;&lt; R_1 + (R_2||R_3)\$ 

if so then you can ignore C1 for the low pass (assume it behaves close enough to a short) and the -3dB cutoff will be at approximately: 

\$f_c = \frac{1}{2\pi (R_3 + (R_1||R_2)) C_2}\$

Note that this assumes low impedance for the source Vin. If it has a source impedance Rs then just add that to R1.