How to (cheaply) maintain a plentiful herb supply
Grow them! It's easy, cheap and they'll always be available. NOthing you'll ever grow will give so much back for so little input.

Many herbs - especially rosemary, sage and thyme - are woody perennials and once established in a sunny corner of your garden, they will grow and spread and you'll have them all year round, if your winters aren't too harsh. Better still the woody herbs actively prefer poor, free draining soils with lots of grit mixed in, so they will grow, look good and be fragrant in sunny, high traffic spots such as the edge of a path, where other plants, even grass won't easily grow.

Buy a couple of growing pots from a good local garden centre and have a go. Parsley is a little harder (it germination can be erratic), but it's a binannual (which grows one year and flowers the next), so once you have a root established you'll get a couple of years out of it. Like coriander leaf it needs sun, but more moisture. If you have a moist, even slightly shady spot, and plant chives and mint, you'll never get rid of them as they are hardy and prolific.

Basil will grow very well on a sunny windowsill if you keep it in moist and rich compost and frost free.

Good luck. Nothing steps your cooking up to the next level like everyday access to fresh herbs.