How can I ascertain what financial compensation I should receive in exchange for my intellectual property?

I have invented an apparell accessory. It is patented. A major company is interested in producing my idea/protoype. Where and who should I consult with/hire to ist me in my negotiations in determining what my financial compensation should be in exchange for my intellectual property? .....As many detailed suggestions would be greatly appreciated! (I really feel like I'm in the dark with regard to this whole area.) THANKS!!!!