I've looked at several DIY jigs for turning routers or hand planers into a makeshift surface planer. I know I could go that route, but if I'm going to that much trouble and expense it makes more sense to just buy an inexpensive surface planer. Or for that matter, pay for one of the more expensive ready made drop tops.
I do have a
Stew Mac Safety Planer attachment for the drill press. But it's a small drill press. I think I could get maybe a 10 inch board planed with it coming at it from both sides. Not wide enough for a full width drop top.
Which is why in my OP I said I'm looking for sources of relatively affordable drop tops.