You were probably talking to the wrong person: either through research or chat you need to ensure you are talking to someone who has the authority to pay you.

Also hidden in your text is "perhaps even written custom code"... could it be that they got what they actually wanted from you and no longer need you?

Finally - sorry if this sounds harsh - if you've exchanged 75 emails and not made a sale, you need to learn to sell better.

Read "Demonstrating to win" (cheesy title but absolute gold for enterprise solution sales), and "Start with No" by Jim Camp (fantastically logical and easy to use way of negotiating that will appeal to techies)

Good luck!