Beats me. A couple of the outstanding lecturers – for example one of the legends in philosophy – only had a BA degree (e.g., http://www.reed.edu/reed_magazine/december2012/articles/reediana/levich.html). My freshman Hum instructor also had only a BA but was an amazing scholar in the classics as well as a poet (http://www.reed.edu/reed_magazine/feb2004/columns/noc/NOC_hanson.html). As folks like that retired, the replacement costs would be higher as the college competed in the PhD market.
But I think the basic answer to your question would require comparing costs at Reed back then with those at other private colleges. Reed’s costs were probably lower even then, but how much lower? But I suspect if you could find costs from 40+ years ago at Amherst, Swat, etc. (other colleges that I considered), and inflated those costs to 2014, you’d see a similar inflation adjustment factor working throughout academia – with COA inflating much more than general inflation. And keep in mind the comparison: for someone like me growing up in L.A., there were many even cheaper alternatives than Reed. Three of my sibs attended UCLA. Two of us went to private colleges (Reed and Caltech). I would have attended UCB if I hadn’t attended Reed. Costs would be probably half of what my family paid at Reed.
I remember that back in that day, Reed’s endowment was only a few million dollars. Then they started to get serious in building it, gradually expanded the college (when I attended total enrollment was about 950; now it’s about 1,400). This implies also a multiplication of administrative and maintenance costs. Back in my day the 100 acre campus had exactly 2 full time people overseeing the grounds. There was 1 dean, 1 assistant dean, and nothing like the proliferation of responsibilities that colleges now have to address to comply with federal and state laws on occupational safety and health, nondiscrimination, disability, human subjects and vertebrate animal research, intellectual integrity, and so forth. This growth of the non-teaching bureaucracy has afflicted academia at large.
I think Reed has maintained its core ethos. Will be heading back for a round-number reunion in a few months.