How about learning a new cuisine? Gok is doing some great Chinese food at the moment and you don't need loads of kit and special ingredients.
Or Indian, this does involve more investment in spices, but if you head to your local asian groer you can pick them up much cheaper than the supermarkets. Making your own bhakis, pakora, dhosa, etc is so satisfying. I love cooking Indian food as it is so therapeutic.
Try some Malay/Thai/Vietnamese dishes. Wonderful fresh vibrant flavours.
Middle eastern, home made hummus is cheap and much nicer than supermarket stuff. Baba ganoush, muhummara, kibbeh, tabbouleh, flat breads.