The cost of doing the floor correctly is nothing compared w/the cost of you falling thru the floor...and the ceiling below the floor and breaking your leg, hip or back.
Of course, that would only happen if you are carrying a 75lb. box of glass Christmas ornaments, and guaranteed that you fall backwards, you land on your ass and the box hits you square in the chest.
Yes; 1" tongue and groove is way expensive, overkill and practically indestructable. You'll be FINE with 3/4" plywood and LOTS of screws. The attic floor doesn't have to be flat or even (unless you're making living space up there). So, get the semi-cheapest 3/4" plywood Home Depot has. You'll have to pick and choose the sheets (bring gloves with you!) to ensure the ones you get aren't totally wavy like a roller coaster track. But in the end you'll be fine.
Can you FIT full 4x8' sheets up into your attic? You might want to measure the opening that you'll use to get them up there. Let HD cut them w/the giant panel saw accordingly. Will save you much grief.