Thanks to both CraigTM and Yllanes for the excellent advice. I did buy Avios on the Iberia Plus site this morning and in fact the deal was even better than Yllanes had said. Iberia is running a promotion until 6th November with a 30% bonus, so I got 130,000 Avios for 1800 EUR. As the Business Class ticket was 150,000 Avios plus 194 EUR, I got my round trip for under 2300 EUR, when the “Business Promocional” fare for the days I am flying is 3918 EUR.

I was initially tempted by the Groupon offer which would have been 100,000 Avios for 1245 Euros, but the FlyerTalk discussion of the T&Cs, including the two-week wait for the Avios to clear and then a 30-day limit to use them, put me off that idea.

BTW, I think you can buy only 100,000 BA Avios per year, but apparently you can buy 200,000 IB Avios. I couldn’t find the T&C on the IB Plus website but, after I bought my 100,000+30%, I clicked through again and the system told me I could buy “up to 100,000 more Avios this year.”

Anyone have experience buying up to 200,000 Avios in a year? At about 1.3846 Eurocents per Avio, it seems to me it’s not a bad deal.
^