Appleinsider has a good review of the Abxylute S9 controller today. It looks like this is the one to beat for a wired iPad Mini controller under $100.
I tried the Galileo G8 modded to open up wider for the iPad Mini, it's not ideal. It's physically awkward to get on/off the iPad without feeling like I'm going to break something. It works but I don't love it. Also, the headphone jack worked initially, but didn't work after modding. Really weird and disappointing, have to use bluetooth headphones now. The wider G8+ bluetooth model looks good if you want a bluetooth controller.
Abxylute S9 doesn't have a headphone jack either, so it's a draw there. I don't have a USB-C iPhone yet, but on the original Backbone I have yet to find a phone case that works with its lightning port, so the deeper USB-C port on the Abxylute should be helpful for phones with cases on.