I can answer for TD. They figure out the drip price on their own and IF - note the IF - you have an account of sufficient size AND you have requested to sign up for "Specials" on DRIPs they simply credit your account and get the discounted shares in a day or two from the transfer agent.
Do not know what E-Trades policies are. There are three possibilities. In neither cases are they "screwing you". #1 - They may now participate in DRIPs and simply buy in the open market - usually at the opening price on the day following payment. #2 - They participate in DRIPs but only handle "Specials" on request. #3 - They do not deal with "Specials". If either #2 or #3 are correct you have two choices - move your account or forget it. E-Trade cannot legally keep a DRIP discount.