It's expensive in terms of time investment (not even really that as each item "creation" probably takes 5-10 seconds at most, but in "waiting" time), but in terms of expensive mounts it's really not that expensive. Undermine Journal puts the (averaged) price of living steel at about 435g and Ghost Iron at around 6g per bar. Which totals to about 14850g and 30 days of waiting.
Other mounts for comparison (again using UMJ data where applicable, and of course applying guild perk discount and any associated faction discounts):
Mekgineer's Chopper: 11250g (Vendor Mats) + 3180g (titansteel) + 250g (bolts) + 50g (fur) = 14730g
Vial of the Sands: 26100g (vendor mats) + 3170g (truegold) + 700g (flasks) + 80g (oil) = 30050g
Grand Expedition Yak: 108,000g
Traveler's Tundra Mammoth: 14,000g
Jewelcrafting "4 color" panthers: ~21,000g each, give or take a few hundred based on gem color
Jewelcrafting Onyx Panther: Just the 4 above combined, so ~84,000g
Again, it's really quite cheap. It's the waiting that is the "expense", I suppose, building up excitement perhaps.
edit: Sort of quoted the wrong person. As you said basically what I am saying (aside from getting the required mats wrong).