To be honest it's useless to speculate, especially when you consider how it relates to the thread. ZUFFA has made it clear they don't want media, fans, or other fighters to know how much they pay, and that includes guys like Khalidov.
When there is almost nothing to off of outside of the absolute MEGA-stars like the contracts of Randy Couture, Overeem, Lesnar, GSP and Nick Diaz that have actually been examined down to specific bonuses and clauses....I doubt anyone can really get a firm idea on how much money they can possibly make in the UFC without being THE guy. And that's not exactly a promising prospect right now with that Anderson Silva guy at the top of the division.
Hence, why Khalidov laughed at the offer and stayed in KSW.
Hell, Bibiano Fernandez is proven and would definitely be fighting for a title with his combination of world class pedigree and athleticism and yet, even HE laughed off the UFC to fight in Japan.
Another factor is probably also these types of fighters like to be free agents that fight in multiple orgs for paydays and easy wins and also alternative sports like boxing, sambo and kickboxing which is not allowed under UFC contracts. Yeah we will never know how much these guys get really paid which is kinda good so the riff raff don't come and start mooching like they do to boxers