You have at least a couple of options:
Remove the dining plan and add it and pay for it at least 3 days before going.
Reduce your park tickets to Base tickets and upgrade them on arrival. In that scenario maintain your Dining Plan and pay for it by 45 days out. I strongly urge that in the end you get Parkhoppers for enough days to match your trip. With a group of 5 and being your first time you'll really appreciate the flexibility. PH option cost $45, no matter the length of your ticket, its a one time fee.
Do the one you can afford. I'd pay for as much as I could 45 days out, simply lessens the stress of vacation and allows the excitement to build.
If you're getting one of those stimulus checks and getting it by direct deposit they are due to go start going out next week. Hopefully that can be helpful to you.
Good luck!