From the autumn of 2004 to the spring of 2009 I kept a detailed spreadsheet of Plus 8's for sale. There were always at least half a dozen available in the UK. In that period, I found 32 2000 model year cars for sale. Minimum price was £27,950 for a Corsa Red (SGT) example with 2,000miles recorded. Maximum price was £33,995 (Berrybrook) for a Connaught Green (4.6L) example with 8,910 miles. This one appeared for sale in May05 and was reduced to £29,995 in August05.
Plus 8's are rarely up for sale now and I doubt you'll see a good one below £30k for a long time - if ever. I predict that the Plus 8 will outstrip early Aero 8's before too long. Prices are already on a par.