
Now Here's How
Harry, Ron and Hermione all created their basic look with clothes from their closets: white shirts, gray slacks/skirt, gray sweaters, and black ties. (Well, we did need to provide a black tie to Hermione.) All of these items came from the closet and cost us nothing. Then they added graduation gowns. One came from my college graduation and two were bought at Goodwill for $2 each. Their wands all came from nature. They each took sand paper and dulled down twigs (for free) to create their wands. All of them needed hair dye to match the characters ($3 total.)
Then each of them added personal character touches:

Harry carried a magic trick and a box of "Ever Flavored Beans" (made by Jelly Belly). The magic trick came from a simple magic kit he received for his birthday. The Ever Flavored Beans...okay, okay, they were the splurge! $7.00 at Barnes and Noble. Another great touch: he practiced various Harry poses and incantations.
Hermione carried a large old fashioned book from her mom's book shelf and a stuffed toy cat from her toy box. She did a great job with the Hermione attitude and had the eye rolling/foot stomping down pat.
Ron broke his wand and taped it together. He wore his shirt untucked. He carried a smaller bag of Ever Flavored Beans (again, splurge $4.50). He carried a toy rat. He could flip a switch, put it on the floor, and chase it yelling "Scabbers! Come back here!" (Again, splurge -- $6 at Walmart pet area.) He wore an old pair of shoes with holes in the toes. He also took some of the webbing from our Halloween decorations, draped it over his shoulders and placed spider rings from one of his school party bags through the webbing (all free.)

For McGonagall's look, things got a tad pricey, but if I'd had more time I think I could have asked around to borrow certain pieces. I bought an old black prom at Goodwill ($10) and a black blouse ($2) with poofy sleeves (since the prom dress didn't have the right top.) Since the cape covered the waist, I didn't need to sew or alter the dress or blouse. I simply wore the blouse untucked over the dress. Then I used a broach from my own jewelry box to clasp my blouse at the neck and my own high heel black boots. Finally, I bought one yard of really pretty green fabric ($3 -- half price sale.) To make it into a cape, I cut it up the middle lengthwise, but only halfway up the fabric. At the halfway mark, I cut a small circle for my neck. Then I sewed a seam at all the edges. (Incidentally, we've loaned different pieces of this for local plays and other kids costumes.) I, too, needed dye hair spray ($1). The BEST part of my costume: the sorting hat! I bought a scarecrow hat at a second hand shop ($5, but major score!) and covered it with batting and brown fabric ($2). I pinned the fabric to the scarecrow hat from the inside with safety pins to make the "dimpled" look. I carried it as a puppet so that I could hold it over the kids' heads and yell, "Gryffindor!"
Hagrid used a shoe box, black paint, and battery powered touch lights from our hall closet to make his lamp for leading the first years. All the supplies came from our house. He wore boots and pants from his own closet and stuffed a Goodwill XL flannel shirt ($2) with pillows from our house. Then he borrowed that awesome coat, a real duster, from a friend of his. He did have to buy a black wig/beard at a costume shop ($7). Finally, we bought scrap fur fabric from the odds and ends rack ($1). We tied them on a string and hung them around his neck as if he'd been hunting.

