This inflation calculator is a great tool for low budget filmmakers. Roger Corman produced a half decent movie called The Evil in 1978 for $700,000. I was curious how much that would be today. I found this site, and I just calculated that for 2010. It would cost $2,313,084.36 today.
I remember nearly ten years ago hearing that low budget according to people who apparently know was then actually anything under 22 million.