Alro is crazy expensive for new pieces, cutoffs not so bad. I had them quote me $220 for 2 - 6'x12" wide pieces press broke into a 90* down the middle (rockrails). I ended up buying from a place in Wisconsin and had them shipped to my house - Total cost was $60.
Don't know where "school" but in Lansing we have Padnos. It's a metal recycling center and they have a large pile of scraps. Alot of it is total junk but you can find stuff for practice and small projects. It's $0.20 a pound. They sell new there too and will cut it to length. Price depends on steel and the cuts (beyond the cut to length cut) cost a $1.00 I think.