I cannot comment specifically upon the Iguana, but I have sold some 40 Caithness weights over the last 12 months, most Limited Editions with box and certificate, in pristine condition. Very few made the original issue price. Lampwork - as ever - seemed to do better than the ugly (IMHO) 'swirls and bubbles' type, the latter achieving maybe 25% to 40% of issue price. I think your Iguana would be a readily saleable piece, but the issue price was somewhat heroic; my guess is you might expect £150 or so - but you never know what might happen on the day.
More generally, I think Colin Terris' estimates of market price were some way off when the book was written, and have got worse as time has passed: in particular, he seemed to think that prices were bound to increase (despite Caithness flooding the market with several million items during their existence), and also that some of his 'swirls and bubbles' creations had appreciated in value far more than Allan Scott's or Willie Manson's lampwork. Wishful thinking, I guess.