May be worth it to get a special belt for deadlifting, but this certainly isn't true for everyone. Maybe get a cheapo 4 inch belt to test it out and upgrade it a little bit later down the line. I still use my cheapo €20 belt and, though I would lift better with a 2.5 inch on the deadlift, I make it work with the 4 inch. Nobody really needs a wardrobe filled with belts, but it can help a lot to have special belts.