Hi Lawrence,
I had excel based linear price and part worth simulators for ACBC. As far as I remember they rescale price parameters after estimation to original scale, so you could use simple linear parameter - but check the ACBC documentation and compare with the SMRT simulation results. If you take a logarithm, you should log. Although I haven't used piecewise for the ACBC I've used it for the CBC with the HB estimation and in the excel simulator price is a straightforward sum of products of price parameters and prices recoded in design matrix (google: "coding price for piecewise").