It's still in the really early days, but from inexpensive self-powered speakers that give your iPod nano earphone-free audio to tiny microphones for voice memos, the news on the cheap accessory front is super promising. So many specialty electronics vendors are now selling through Amazon and eBay, and they provide websites with reasonable prices and shipping from the Far East.
Auntie hasn't had a huge amount of time to test out or acquire nano accessories yet, but as with any iPod line, there are already more accessories for nano than you could dream of or hope for. Many of them are both useful and cheap, just as you asked.
Auntie has placed an order for one of these US$2.49 microphones (with free shipping) for her new nano, with the hope that it will work as well for voice memos as buying a standard iPhone earbud set. The iPod nano's built-in voice memo support has been a stealth feature that a lot of new owners have overlooked; the onboard application does not appear until the nano detects a microphone.
Amazon sells branded iPhone earbuds for around $16 (normally they go for $30 at the Apple Store) as an optional accessory for the nano. The standard earbuds provide both a built-in microphone as well as an external playback squeeze control. Auntie has a bunch of earbud units on-hand, but they're awkward to use if all you want to do is voice recording in class or at a meeting.
Hopefully, the little plug-in mic will work with the nano (as it reportedly does with the iPod touch) to allow voice memo support, but since the mic has yet to arrive, Auntie can't yet evaluate the product.
Auntie does already have (and has been using for years and years) this $7.67 plug-in speaker from DealExtreme -- ever since her first 5G iPod video. Operating through the iPod nano's dock connector, the simple speaker provides only basic audio quality.
It's perfect for playing audio books in the kitchen while banging around with pots and pans, but don't expect to cry at the beauty of a symphony. The tiny footprint and the firm coupling with the nano make it a great accessory on-the-go.
No nano accessory post would be complete without mentioning the nano as a fashion accessory. While you can easily fit the nano's clip onto a cheap watch band from the dollar store (cost, as you'd expect, $1), Auntie's nano has also acted as a tie clip (don't forget to use the multi-touch rotor gesture to move the interface orientation into alignment with the tie), a hairband ornament (hairbands are six for a dollar at the dollar store), and as a necklace pendant. (Speaking of which, the nano makes a really sweet name tag, too.)
Oh, and one last thing. You know those old original iPhone docks? They work perfectly with the nano. Most docks do, for that matter. The nano is small enough that the original footprint really has no effect. If you've got a dock with built-in speakers or video out support, or if you can easily acquire a second-hand unit, you might consider pairing it with your tiny nano.
Got any other accessory suggestions for Cousin Stephano? Let Auntie know in the comments!