If you experience bad mouth ulcers, you're probably already familiar with Adcortyl in Orabase - after all, it's what the doctors prescribe for them! On prescription this costs £7.10 in England. In Scotland you can get it in Boots over the counter for £5.90. Online, chemist-4-u sell this for £2.93 + £2.95 delivery - BUT if you order two or three, you only pay ONE delivery charge. I just bought three tubes for £11.29 inc. delivery.
This stuff is WAY better than the branded alternatives such as Bonjella. If you've not tried it, the trick is to apply it as soon as you feel the ulcer coming, and use it every night. It really is the best out there - try googling it if you're unfamiliar!
Remember, buy more tubes for a cheaper deal to save on postage!