A quick Google search suggests that reverse osmosis will take fluoride levels down by an order of magnitude, and although under-sink reverse osmosis filter output is indeed "way more expensive" than tap water, the difference is negligible as long as you only use the filtered stuff for drinking, while still bathing, cleaning, landscaping etc. with unfiltered.
This all assumes you actually want to remove fluoride from your water, though; I still haven't seen any decent evidence suggesting you would.
You would have to do more than that; for example, you would have to avoid any toothpastes, obviously, but less obviously you would have to completely cut out tea and some other plants which naturally contain high levels of fluoride. (Tea would be a real sacrifice for me.)
I've recently learned about alleged dangers to drinking fluoridated water. Amongst them is increased rate of cancer and lowering of IQ. Interestingly enough, wiki doesn't mention this at all, but searching for it brings up a decent amount of (what look like) reasonable results. I am really curious about this, and want to learn more about this. I was wondering if anyone on LW has already conducted a research literature investigation on this topic, or if you just have tips/advice on what to pay attention to when I read the literature.
Thanks!