Can someone recommend a radio with an Aux/MP3 input

You can check eBay for a stock unit from maybe a 2008 prius, which should have aux output on the radio

 

If you haven't thought about them, you have 3 options really:

1. Aftermarket CD player - two options here - replace stock CD player with a double DIN using a kit or put in a stealth CD player where the current plastic "cubby" is below the CD player. It fits a single DIN perfectly, just need a couple of screws (I know because I did this on mine). Be sure to see this thread for getting the right wiring adapters: Stealth install an aftermarket stereo in Prius | PriusChat
2. Drop in a CD player from a later model Prius with Aux in (I think 2007 and later, could be 2008). Obviously, you'll need to install the aux in cable/port as well.
3. Add an aux in to your existing player. A poster in this thread was able to do it: Cheap and easy way to add Aux input on '05 Prius? | PriusChat There are several companies out there that offer kits; do some additional Googling if you're interested.

If you're going with option 1, I'd just look for a name brand CD player with at least 10W rms output per channel with a 1/8" input. Something like this. Definitely no need to spend more than $75 for a quality CD player these days. Consider getting one with a USB port that can read thumb drives if you might use it. This is really nice feature these days.

Also, check that you don't have the JBL system. If you have the JBL system the speakers have too low of a resistance and aren't compatible with 99% of CD players. You can tell you have the JBL system by a middle channel speaker being there that's behind the center screen . If you have a JBL system and just want a line in, I'd go with option 3.

 

Look at the picture I posted with the aux button on the radio, your eBay one doesn't have aux button

 

On Pri-i like mine, it's inside the arm rest storage between the two front seats. So you would need to get the cable or a 1/8" plug for it (but not necessarily install it in the middle armrest.

The sound quality on those tape adapters isn't very good. If you're going that route, just get a well reviewed 1/8" fm transmitter and use your current deck. The sound quality will be about as good, at a much lower cost. It's probably worth trying first anyways and you can decide if the sound quality is good enough for about $20. Just don't buy a super cheap one of these - go with one that's well reviewed.

 

I use something similar to this in my 2005. It's not the greatest of quality but it gets the job done cheap and easy.