He wants the fight in the UK because like so many US fighters Taylor doesn't actually know where his passport is.
I would suggest 800+ based on the fact the fight will easily pull in enough to give him that payday and with the Uk ppv's alone he'll deserve it. No matter what we think of the guy here's the facts. He's the WBC Champ. He's Undefeated, standard of opponent is poor agreed but 24-0 19ko's will get quite a few ppv's in the Uk. Taylor needs this fight as much as Froch. Pavlik dominating him and a win against a Lacy who hasn't been the same since Calzaghe is hardly huge demand making material. Of the top 6 Super mids out there Froch is probably the weakest or should I say untested. If I was Taylor I'd be crazy to not give Froch 800k at 60/40 or 55/45. A good payday, possibly win the title, beat an undefeated fighter and raise his profile all in one fight? Hell yeah.
After his super display of power vs Pascal, i dont think he will draw big crowds in the future, so, I say 500K$ should be enough for him to accept such a big fight.