Low learning curve and bang for your buck don't necessary go hand in hand. Normally, I'd say squat variation, deadlift variation, press variation, row variation, but the first three are all pretty technique heavy (rows are too, but to a lesser extent). Now obviously there are variations that are less technique-heavy and have a shallower learning curve than others, for example, a conventional deadlift isn't as demanding technique-wise as sumo deadlift, but the conventional deadlift still is a technique-heavy lift and to dismiss the conventional deadlift as "grab the bar and stand up" is going to miss out on a lot. Still, they're going to be easier to learn than Oly lifts and will be excellent from a bang for your buck standpoint.
I'd pick at least one from each category, but you can always change it up every so often (change them less for a beginner athlete who has to learn the lifts).
Squat variation: low-bar, high-bar, box squat, front squat
Deadlift variation: conventional, sumo, trap bar, rack/block pull
Press variation: bench, incline bench, military press/OHP, DB bench, DB incline bench, DB OHP
Row variation: Pendlay row, bent row, chest supported row, T-bar row, pull-up
Obviously there are other variations but I'm not going to get super fancy here and I don't see much of a reason for a beginner who you're trying to find bang for your buck exercises to do Zercher squats with chains or snatch-grip deficit deadlifts against bands or whatever. Keep it simple...while there is a lot of technique involved in some of these exercises, they're still the kind that anyone can learn and are more beginner-friendly than the Oly lifts IMO.