Your job, everyone's job, is to make your boss look good.
Your boss wants to use up his entire budget, and deliver a working solution as promised. There doesn't have to be any connection between those two. I think that the gpp was proposing that you help chose a proprietary system which would burn up the budget, and that you use you spare time to set up a F/OSS system which would work.
When the proprietary system fails, put the free one on to cover the gap. Now that it's working, it's pretty hard to argue that it can't do the job. Your boss has used the money, he's gotten the kickbacks from the salesmen, he's delivered a solution, you've made him look good. As long as he gets to take credit for everything, you'll be sticking around.
Those are your knowledgeable users, who read and understood your message.
If you would know the value of money, go try to borrow some. -- Ben Franklin