Waiting until the last minute, whether it's shopping for Christmas or a vacation on the beach will usually cost more. I hate to put it off, because I won't have time to shop for bargains, to compare prices, to wait it out to see if I can find something better (cheaper, better quality, bigger...).
If you're waiting on a pay check or something else prevents you from starting yet, don't just sit on your hands. Look around, decide what you want to buy and find best prices while you're waiting. Then when the money comes, you'll know where to go and how much it's going to cost.