Having trouble with if function

i have a form that calculates all services together

IF(services>640, maxprice, servicefees, IF(services<64, minprice, servicefees ) )

like so what i want that if the fees is less then 64 then it shows minprice if they are bigger than 64 they show servicefees together but not more than 640

http://wordpress.org/extend/plugins/jazzy-forms/