When we redecorated our house, we went to our development corporation. We pay into the account every year, and had never used any of our reserves from it. So we ended up getting about $600 and bought paint, slipcovers for the furniture, new rugs, and little accents for the rooms. One sister, who could sew like a champ, made curtains from plain old twin sheets that cost like $4 a set. It ended up coming out really nice, and we did the kitchen and living room. It was like our own trading spaces
Also, get parents to donate...if someone's daughter is living in squalor, nine times out of ten, they'll throw in $20 for some paint.
Finally, make sure that you do something to spruce up the outside as well. We ended up planting flowers in big clay pots for outside the door, and they really jazzed up the porch. Simple, but very effective!!
Good luck!