Lots of things! And cheap things are fun! For your $75, you could get:

-a Monotron Delay

-some contact mics

-a Gakken SX-150

-a small glockspiel

-patch cables for your new Model D

-any of a number of cheap guitar pedals

-a Stylophone GenX-1

-an Otamatone

-a crappy melodica

-or, for just a hair more, a very cheap theremin

But if you don't have a particular need, or if nothing is striking you as fun, I agree with u/tbqhfamicom -- might be best to save your gift until you can put it toward something you actually want.

ETA: Oh, also, if either the Minilogue or the D takes an expression pedal, that might be a good investment, too!