Cosamin is cheaper and exactly the same thing. When I was using this for Sophie I got my best deals on Ebay. Just make sure you are buying from a US seller and you buy only product that is still in the sealed box.
I was paying average 23.00 total per bottle of 108.
I bought at vitaminshoppe.com - it is $37 for 150 pills. Spend $100 and shipping is free. And search online for coupons - they are always running a coupon for $15 off a $75 order.
Edit - this is for Cosamin DS, not Cosequin DS.