Yes, you will have to show ID with the resident tickets, so if you are not a resident, that is not a solution.
You should also avoid things like buying tickets on EBay, as you can not be sure that they have any valid admission left on them. There are some honest people out there, but if you're on a tight budget, you can't afford to get to the gates and find you have no admission on your tickets and have to buy them at the gate.
Bottom line, you are not going to find any deep discounts that are not tied to a timeshare tour. You will find some legitimate ticket wholesalers that will give small discounts on the multi day tickets, but you will be lucky if you find more than 10% off. If you are an
AAA member, you can get some discounted tickets through them as well.
My advise would be to not buy any more ticket than you need. Do not buy the park hopper option - plan to spend the entire day in one park instead. Don't buy the no expiration option - plan to use all your ticket days on your trip. If you are going for several days, but only plan on visiting a water park once, don't buy the water park add on option - just buy a one day water park ticket instead. By tailoring the ticket to the minimum basics you require, you will get the best value and not waste any money.
Theme park tickets are expensive, and there aren't a whole lot of ways to make them less expensive. You are better off working on the other costs of your trip (like food and accommodations) to keep the overall cost of your trip within your budget.
