If Falcao is as bona fide as he has looked in Europe (for the last 3 seasons) and what we're seeing is his actual level - and thus far, there's nothing to say it's not - then we're looking at an all-time great in the making and a player who will go down as one the greatest strikers in modern history when all is said and done.
In today's market, and with what he continues to do on the pitch, £50m - £60m should be his fee. No bones about it being an astronomical amount, but again, if this is his level, he is truly an elite striker who can turn a game in an instant against any opponent in any competition. Players of his class are gold dust and all of them would be bracketed in the same band or above if they are or were his age:
Rooney, Villa(peak), Ibrahimovic (was valued at 65m in Barca move), Van Persie (of the last 18 months), Eto'o (peak), Drogba (peak), Tevez, Aguero, Benzema... Falcao isn't out of place in that company.
I guess a couple of problems he has that are out of his hands are that he plays for a crap NT and will never get the chance to light up an international tournament and he hasn't had the chance to wrack up goals in the CL to verify his pedigree, but from his movement, finishing and all-round game, there's no way the CL would effect him.
Atletico paid a fortune for him, and rightfully, anyone who wants the player will be quoted an astronomical price because he is an absolute gem who keeps on proving his class and looks to be improving and is not even at his peak yet.
For the price he will cost - unless he'd force a move to one of the Spanish giants - I can't see anyone but City, Chelsea or PSG acquiring his services, unfortunately.