Join Date: Aug 2011
Location: Barcelona, London, on a plane
Programs: IB+ Gold, TK E+, Hyatt Globalist, Marriott LTP, IHG Diamond
Posts: 14,182
I haven't looked recently, but Scandinavia, Dublin were usually the cheapest, followed by Spain. INV and JER as well were sometimes good options.
Of course this is actually more relevant to AS/AA/etc. region-based charts, as the cost of positioning to many of these places plus the extra Avios from these places back to LHR outweighs the YQ/tax savings...