depends on the brand. I did a research weeks ago, and found out lens.com is one of the cheapest websites to buy contacts. I am with VSP plan which covers 120$ allowance of contacts if it is in network. Lens.com is out of network, but I still can get 90% of the money back. ( it worked last year). And also it's FSA eligible :)

www.visiondirect.com. They are cheaper than 1800-contacts and always has promotion... FS with $100 order ( i think).