I like 55% low-multiplier (but current tech) engines, and devote the rest to fuel tanks.
OK-ish speed for reasonable cost, practically unlimited range, useful as a secondary tanker.
It may be worth to prioritise the minimum power tech line.
At 10% power, maximum-size drives cost the minimum of 5 per engine up to Internal Confinement Fusion, and you greatly cut your crew requirements - relevant as crew spaces are actually fairly expensive per ton compared to cheap bulk.
Tech investment is modest considering what you need for a decent jump engine, and it has other applications too - e.g. tugboats capable of hauling massive planet-built stations at a decent speed without undue fuel consumption.
If you absolutely don't want to spare the tech investment and have no secondary requirements for your mobile jump gates, low-tech low-power engines as in your current design make sense even though it's not pretty.