Yeah, I paid over $100 for the last replacement, 1/2 micron filter. No idea if the 1/2 is over kill or not. Probably is because my bro is a bit anal. But it's good for 300 gallons so I figure 1 a year isn't killing me.
You could probably replace yours with one of the penteks and write me a check for the difference.
1/2 micron @ $100 is overkill in my opinion unless you have some serious gains from it. If you're worried about bacteria, etc....yeah. Otherwise, I'd just rely on your water supply to have enough chlorine in it to take care of any threats. If you have a hot water tank, you could worry about Legionnaires' Disease, but you can make a few system changes to make that less likely.
5 micron is about as small as I'd go....they typically will do 8,000 gallons. You really just have to see if you're dealing with hard water or what you're trying to filter out. The more filtration you do, the more frequently you have to replace your filter...and the less water pressure you'll have at your faucet.
I filter all of my incoming cold water to my water heater using a 10 micron filter. My cold water under my sink is filtered with a 5 micron paper filter.
I've also used these whole house filters to infuse homebrew beer and quickly filter yeast out of kegs for a more stable product without having to use additives.