Those are 100x more expensive than a cheap air pump.
I have a wide variety of air pumps, but I rarely use any of them because those little air bubbles they create also splash water around the area your tank is located UNLESS you have a tight fitting lid.
What make & model is your 15 year air pump? I'm always fascinated by old school aquarium equipment. I have a Penn-Plax Silencer & it's probably older than yours, that my friend gave me. One cool feature about it is it has a adjustable air flow thing.
I just took pictures of mine, but there's someone selling it on Ebay as well, so here's a link to give you an idea what it looks like.
I wouldn't recommend buying this version because of it's age. If the rubber flapper/plunger inside is cracked, it's not going to be easy to find parts for it.
If you really want a new air pump, search CL for yard sales/rummage sales/church type sales.
I got the orange kritter keeper cage that I nearly melted, with an orange octopus decoration, a small fish net, dirty gravel & unopened jar of fish food for I think less than $1.
Otherwise the cheapest air pumps are generally quite crappy and will still cost you at least $5.
Since your pump works but creates a lot of noise that bothers you, just keep an eye out for a yard sale.