I know you're short on time, but I've bought oil before from Opieoils, via web order, and their prices are generally competitive. Last time I got 4 ltrs Fuchs Titan Supersyn 0w 30 506.01 for a little over £30 as it was on special offer. They might have an offer on 505.01 if you look. Only trouble is 4 ltrs might not be enough for all engines, and it might not arrive in time for your wedding etc.