If you haven't registered the account yet, you can try to sign up again with any promo code available in the Internet.
You should see a text field for you to enter promo code during the sign up.
Sometimes a promo code may be saved in your cookies and automatically appear in the form during the sign up process. If you want to enter your own promo code, you can try to clear the cookies and sign up again.
And unless I've missed something, I don't think you can get $1.8/mo hosting service. DH offers maximum $50 cash discount for new customer. You can get some free domain names or IP address though.
$50 off and 3 free domains with code: [color=#CC0000]DH3[/color] [url=http://dreamhost.com/r.cgi?296804/signup|DH3]Sign Up NOW[/url] or More Codes Here