I saw the above suggested in LEO on the Cheap. In P.130 it says:
A compromise between high-performance/lightweight pump-fed vehicle designs and cost-optimized pressure-fed vehicles with heavier structure is a possibility, by using pressure-fed engine designs with simple, low-pressure turbopump assemblies. This approach retains the simple, inexpensive engines typical of pressure-fed vehicles, but it uses low-cost pumps to avoid the heavier pressurized tank structure needed by pressure-fed boosters.
So basically we get 15-40 bar chamber pressure, fueled by a pump that could have been mass produced for a jet engine - or a diesel engine!, and relatively light tankage.
So, who has tried to do this on a rocket with the purpose of reducing cost (of course there is an example in the book) and what was the outcome?