Looking at Quill youtube video. In classical era machinery (medieval era tech) cost 360. When he reach medieval era the same tech cost 300. So tech rushing one era ahead will have a cost increase of looks like 20% and likely even bigger penalties the futher ahead the tech is from your era. There also seems to be a tech cost reduction for researching techs an era behind. So it is more expensive to research ahead while it is easier to catch up both due to the penalty as well as the cost reduction. Industralization in the medieval era cost 1014 from a base cost of 700 which suggest that the tech penalty is 1.2^a a = numbers of eras ahead.