This one: http://www.retrobike.co.uk/gallery2/v/M ... 1.jpg.html
They look like compact chainrings. It'd be cheaper to replace the chainset with something like this for example: http://www.chainreactioncycles.com/shim ... -prod46021
But you'll need a new chain: http://www.chainreactioncycles.com/shim ... -prod86120
I expect, as they'll be equally worn. To do the job you'll need a crank puller, chain tool, freewheel tool and chain whip.... all of which adds up to a fair whack of cash! You'll be lucky if the new cranks fit the old bottom bracket too.
If you can find a used equivalent chainset with less worn rings in the For Sale pages then you might do ok, though the amount of wear on the chain and cassette is still of concern.
"Sometimes glass glitters more than diamonds because it has more to prove" Terry Pratchett