I would say yes its too much for simple powder coating.
My last set of splitrims with magnesium lips only cost me £520 from Mike including him:
Arranging courier to and from glasgow where he is based
Splitting the wheels
Welding the magnesium lips where curbing had occurred, then mirror polishing them (Cannot even see weld)
Media blasting centres and barrels
Welding damage on 1 centre
Powdercoating 4x centres in RAL-6018 bright green
Powdercoating barrels in gloss black (Inner and outer)
Ceramic polished bolts
Lacquered centres to make the green colour more vibrant
Reassemble the wheels in correct manner and correctly torqued bolts.
So for a place to charge £125 per wheel for simple powdercoating thats why I think its expensive.
Pic of my wheels when done
And over 15 months later (Car used daily)