Angle grinder gears are by far the cheapest way to source semi-decent right angle reductions. Limits things to about 2.6:1 in the right angle stage at most. To get in the region of drills, say 30:1, you'd need a further 11:1 reduction, which you won't get in a single stage after/before the grinder gears. You'd need three stages. This is the issue I face with Rango, as it happens.

You could get a pair of Bosch 35s for cheap, whereas triple-stage custom 90deg gearboxes could cross into the hundreds easily. I'm sure someone has some 35s.