If you are still in school you could join their Dreamspark program and get Windows 8 free of charge. If you don't qualify for that you can still get a free developer token by simply joining: https://devcenterbenefits.windows.com
The Windows 10 preview that's out right now works well enough for casual use today. I've been running it on my laptop since it was available and have had a few minor issues, but haven't had any real trouble using it as my primary machine outside the office.