This was a hypothetical question I came up with while playing with the research rules. The base cost to upgrade lower tech items is min. x15, max x90, average x50. That gets expensive fast if you are determined to get good results (aka trial and error or damn these dice are cursed).
Starship electronics and fuel processors come to mind right off, most everything else is covered in the TL adjustments built into HG. Some things I don't see as able to be reduced such as staterooms, libraries, workshops and Biospheres. Maybe reduce the tonnage on low berths to allow more per ton at a reduced power requirement, not to mention increase the battery life in case of pesky emergencies.