The cost of transfer was included in the rate that was on the interline waybill. If it was a national zone rate, the D&RGW many have had a additive if it was under a certain weight or price. In most cases it was all included in the interline shipment and the Rio Grande just "ate it" as just operating expense.
RWR told me he knew the transfer rate for logs and pipe was very low going through Alamosa as the machines where there. He felt that that transfer rate was so low, logs could have been shipped from Cumbres to South Fork Saw Mill with out much restricting additive. But that was a interline movement they could control the rate of the whole move and fit the shipper needs.
Cars coming from Detroit, were on a national Zone rate and it might have been the same to Durango as to Williams, regardless of the transfer.
We will only know if someone gets into the Trillion of Rate records that moved to Colorado when they closed the ICC. Lots of luck. Some Agency Dept. folks can surely better this reply.