can i then give my checkride on any ME aircraft?
Yes
my guess is it's cheapest to get rated on a dual piston and then give my check. Is that so?
You would not be rated on a ME airplane until you pas the checkride. Not sure on current prices but it used to be cheaper to do the training and checkride in a light twin.
Can i book a a320 simulator and give my flight check on that? Or would i have to get the rating endorsed first
No. To take the checkride in a sim representing an aircraft requiring a type rating you have to show you have completed an approved course of training.