Where to buy a cheap compost bin?

[SuperBunny]

2 questions actually - is it possible to buy a compost bin for less than 30 pounds?

And can I compost on a patio? We have lots of food scraps (veg peelings, tea bags etc) as well as sticks and leaves and stuff that blow onto the patio.

TIA

everything I've read about composting says that you need to put it on ground/soil not patio flags - so that the worms and bugs can get at it and do their stuff.