I felt the same when I found out about this shortfall of my home water filter. Luckily I found a pure water in the supermarket which only costs about $6 for a 10 litre cask. It depends where you are in the world but if you can find a pure bottled water in bulk you might find it affordable, and cheaper than distilled at any rate.
If you can't find pure the next best thing would be spring water. Minerals aren't the best thing for a fast but are better than fluoride!
Good luck finding something better.