How electronics savvy are you?
You can build a full blown air fuel gauge fairly easily for like $15-20.
The display driver they have on there that you can get for free isn't really free because of what they call a 'high demand' for the product samples. National charges $9 for one unit and I think $15 for 5. I got three of them(should have gotten 5).
But you know, looking at the circuit they've put together there, that's simple as hell. AND www.st.com
offers free samples of the LM311 chip used in it. I've got 3 on their way!