If you don't need much power/speed on the drive, and wait for ranglebox restock for your final version anyway, the neptune-28 could be an alternative to the saturn-16.
They're not listed in the shop, and also out of stock (ellis hasn't much time for the shop with robotwars going on, last info i got was "early next year" or something like that), but smaller and lighter.
So for a feather that doesn't want to push or be really fast, they could be an alternative. Planning on using them, too.

Neptune Gearbox Maße.jpg

Just take in mind they have a 28-1 gear ratio, not the 16-1 of the saturns. Sooo... either faster motor, bigger wheels, or slower bot.