HI Mama-
As a child who received the leftovers, I can tell you that it totally sucked. My sister (older) got everything new. I understand the concept (and did then, too) that it was wasteful to buy me new stuff when her old stuff fit me perfectly fine, along with friends clothing that was passed on to me. And then my little sister, because by the time she got there the clothing was worn out, always received new clothes, too.
This is a hard one. My suggestion is to go 2nd hand store shopping for jeans, t-shirts, and whatever you need for the boys. THEN get each boy a couple of brand new outfits or pairs of shoes- whatever you can afford.
For the baby girl, you have to buy what you have to buy. Let the boys know that unfortunately, babies grow so fast that you have to replace their clothing all the time. And when she gets to be their age, she will be wearing hand me downs, too.
One last option is to buy each child a few new outfits and then costco shop or bulk buy things like jeans, t-shirts, uniforms, etc.
I also say that if one will have the most options, but they are not "his" and he has an attitude about it, then get rid of the clothes...take them to Goodwill or Salvation army prior to shopping and let the boys go nuts.
Okay, so now that I have gotten over my childhood pettiness, the deal is this: everything is "new to you" and needs to be seen that way. If you cannot afford new all around, you can't afford it. Are you opposed to second hand? My hubby told me that when he was growing up his mom bought him a new pair of jeans, a new pair of slacks, a new t-shirt, a new dress casual shirt, and a decent pair of shoes or 2 at each school year. The rest was either hand me down of 2nd hand, but the few new items made him feel like a brand new man each year. The rest didn't matter.
I hope that somewhere between my chatter there is something helpful!
Good luck!
-E. M