The cheapest I could find XP Home for, was �64, but I reckon you could get it a bit cheaper if you searched around.
https://secure.softwarepricebeater.com/software/shop/buy_online.php?crn=67&action=show&show_products_mode=cat_click&OVRAW=WINDOWS%20XP%20HOME&OVKEY=windows%20xp%20home&OVMTC=standard