I don't know a source for second-hand vanes, but on a 2 tonne long keeler you will be a bit tight for space for one of the larger items like a Monitor, Hydrovane or Aries. Possibly the Navik or something like that would be suitable?
I managed to pick up a secondhand Navik a couple of years ago and fitted it to a Halcyon 27 that I have since sold, it worked brilliantly. I paid £300 for it. you quite often see them advertised usually around the 5-600 mark.
If you see one advertised don't waste any time as they go quickly.
I saw mine in YM and went for it. They go very quickly and usually in the £500 - £700 range. Easy to fit, couple of hours. I have photos if you need an idea butbest to have a look at a yacht with one fitted. steve@albinvega.com