Go to ebay, find aquadisestore. They are the cheapest one - $2.99 each, free shipping.
I have ordered 12 plants from them by 3 orders. Quality is from ok to good, and no loss so far, all are survived and growing.
But, one problem for the site is, for each order, I received one wrong plant which is not ordered by me. I have to send email with picture to request the right plant that I bought. They did ship me the right plants for the first two orders for free, but not for the third order - so far. Anyway, I have ordered and paid 12 plants and got 14 plants so far.