That's even true if you use regular toilet paper, because you'll need a lot less of that.
Asterisk-mart sells 48 sheets for $4. If you go macro first with regular TP and thus use one wipe per session, folding it over as needed for coverage, let's say you max out at $6 worth of wipes for a month because you don't know you're sensitive to gluten yet and you also wipe up some cat vomit every few days.
That's still only $72 a year, man.
Now: How many bathrooms does your house have? Let's say you have two bathrooms and want to use both. $500 on toilet seats? Better hope you're not a 300 pounder who rocks back and forth a bit when he's in a hurry, cuz you don't get Apple Care with those seats I'll bet.
If you travel every once in a while, or need to use bathrooms at work, there's that factor too.
You didn't include the regular TP. With a bidet or washlet, you'll need a lot less of that, too.
> $500 on toilet seats?
There are much cheaper options available. As another commenter mentioned, you can get a non-electrical attachment for as little as $30.
For example:
http://www.amazon.com/Luxe-Bidet-Neo-110-Non-Electric/dp/B00...
Edit: Also, you were comparing the price for upgrading two toilets with the wet wipes expenses for a single person.
If I catch someone traipsing to the restroom with a box of wet wipes under their arm, they're not going to make it without being made fun of. Sorry, princess, but your anus isn't really all that special.