If going with more gear is your answer then it would be tough to deny the bang for the buck value from Paul C. Buff products.
A reframing of the question and situation might lead to asking what the problem with the chosen location was? From the way that you are describing it I am getting the picture in my mind of a bright sunny day and that you placed the people in a rather deep shady spot while having a bright background. That is a tough situation and will require a lot of light be added to the people, combining images in PS, or moving to a different location if possible. Sometimes walking around the subject to change the background to something darker is an option. Walking around trying to find those pockets of good lighting in an environment is quite the game of hide and seek. If you are up for the challenge of learning what to look for I should think that 'Picture Perfect Lighting' might be of help.