You get what you pay for.
I use tilton pumps and have never had any problems with them. I did a fit out for a GTR recently using 4 of them (2x diffs, transfer and hollinger transmission).
They are not cheap but well worth the money.
The ones I'm using are far from plastic, the pump section is machined alloy with tools steel gears and the motor section is steel.
You want to use a pump that has a separate pump section which is sealed from the motor, tool steel gears and then decide if you want a constant flow pump or a triggered pump (they are different motor sections) triggered pumps has a capacitor start feature so they don't draw all the current away from ecu, injectors etc when they turn on and off constantly.
You want the oil sealed from the motor for a few reasons.
Less heat around the comuntator, brushes etc.
No chance of worn comuntator, brush etc getting into the diff oil
Serviceability you can replace parts not a whole unit
Tool steel gears are a bit noisier but there is massive amount of wear with brass gears which leaves brass in the diff oil.
Tool steel gears will probably outlast the car unless they ingest something.