As an ex list member allow me to spout off.
Where on earth does it say that the D&RGW didn't have the money to buy more K-36's??, none of the paper work that I've ever seen mentions that.
A retired Boilermaker form the D&RGW told the story at the old Mile High Railway Club about the 37's being built to see if they could improve upon the 36's, as they had bought lots of new Standard gauge power, there was a surplus of smaller power to work with. And as none of us were at the meeting when the decision was made I guess we can never know for sure.
A new K-36 cost $27,950.66 (480-489) 1925
A new K-37 cost $24,905.15 (490-495) 1928
A new K-37 cost $22,527.20 (496-499) 1930
The Grande was spending some good bucks during that time, rebuilding most of the Narrow Car Fleet and rebuilding lots of the mailmile west of Salida, so they had money, now the middle to late 30's is another story.