RAW there are no rules concerning extra lifestyle/gear costs for pixies.
On one side you have a general lowered cost because a pixie wouldnt need to eat as much as a metahuman, nor require as much space.
On the other side a pixie would likely need custom tailored clothing/armour and equipment, driving the costs up.
The easiest thing would of course be to rule that those 2 factors would rule each other out.
Note: while initially I think it would be fair to charge extra for equipment like weapons/gear and armour. This has the added drawback of making the pixie even further invested in the classical mage/mystic adept role. As those wont need to spend a lot of resources on weapons/gear anyway.
So, personally I wouldnt make gear/weapons anymore expensive than normal.
But I would most likely also rule that a monofilament whip would deal a bit less dmg, mostly because a pixie likely would have a harder time of swinging a whip the same length as a human would. Thus lessening its Damage potential.
I would try together with the player to find the golden spot, where the monofilament whip isnt an automatic choice for a pixie, yet still a competitive choice compared to a spellslinging pixie.