Yes, freight shipping is a killer. Most freight companies want around $110+ minimum for any shipment so you need to buy enough to get way above the minimum. For instance, 5 boxes of heavy picture frame moulding costs around $180 to ship halfway across the US, but one box is typically $110.00.
One recent surprise was a Fedex ground shipment of 2 heavy boxes from Universal Framing Products for a total of $71.00. That seems like a great deal. Might be worth looking into Fedex ground for glass shipments, your supplier will likely automatically go for a high dollar freight company.
BTW if you do wind up using a freight company be SURE you get a quote beforehand. Those guys have a "standard" price which is around 3 to 4 times the "discounted price." I once got billed $700+ (by UPS Shipping) for a three box shipment, fortunately we were able to negotiate down to $160.00, which was still a slight rip. A good supplier will negotiate a decent freight price for you, but some will just throw you to the wolves! Ask beforehand if you will receive a negotiated shipping price.
BTW2, if you have a local framing products supplier order through them. Local suppliers usually don't surcharge for shipping. Could be worth a short drive to pick up, and some suppliers even have free delivery in their areas.