Not so long ago, Tesco were selling their 'Value' curry sauce (in 390g) tines, for 4p. It was an excellent product, producing a mild, creamy curry, packed with sultanas and onions. Alas. it's no longer stocked, but if Sainsbury's (who, I seem to recall use the 'Basics' name for their cheap stuff) are selling something similar for 9p, I'll certainly be giving it a try!
It's also worth noting that the 'Value' (or similarly-labelled) pasta sauces, in jars, which the supermarkets stock are an excellent base (on their own) for a cheap pasta meal, or they can be used as the starting point for something extra tasty (by adding additional herbs or spices, for example). Morrisons do a really nice one with mushrooms in it.
Chris