They sell them in garden centres, with the cactuses (cacti??!) etc. I'm not sure how much, H2B thinks maybe £2 each, then we could decorate pots ourselves, but not entirely sure - they might be more expensive!
Found them on the internet for £1 each! http://www.sempsbypost.co.uk/apps/webstore/ This doesn't include a pot though, but how much is a plain plastic plant pot wrapped in brown paper, like the first picture above? Hmm. I quite like this idea!
I don't think they would be expensive at all! About 2-3 for the plant and them some plain brown paper and string. The would look fab. If you used them as place setting like the example you'd have a little more budget for them maybe?