Having a service do your shipping will always double, triple, or (in this case) quadruple your costs. Is this a UPS store? They have huge up charges.
If you don't have a guitar shipping box, you can usually get one from a Guitar Center/other store for nothing. Pack it yourself, ship it yourself, and you should be able to do it for less than $50.
(Here's how overcharged your price is; I shipped an acoustic bass guitar once. Because of its size, I had to make a Frankenbox from 5(!) regular size guitar boxes (I was double boxing since it didn't have a hard case.). The end box was close to 5' tall. I took to a FedEx outlet and because it was oversized, it cost $115.)
If you absolutely can't find a shipping box, let me know and I'll send you one for the cost of the shipping, and you'd still be way ahead of their price. But, you should be able to find one around Seattle.