Your looking for a fabric cleaner right? Having used both of these products they work great in my Insight, and should work equally as well on your Prius. For something thats easy to find try Meguiar's "Heavy duty Carpet and Interior cleaner". It's in a pink bottle and you should be able to find it at one of your local automotive parts stores. The only down side is you'll probably need several bottles to do a whole interior, carpet and all.
For a more economical product if you don't mind a little bit more of an initial expense Meguiar's Detailer line has a product called "All Purpose Cleaner". The smallest size this product is available in is a gallon, which is about $15 (compared the the 16 oz bottles of the above product which are $5 each). But really you get 11 gallons because the all purpose cleaner is concentrated and dillutes 10:1. It will do the same, but you can also use it for general purpose degreasing as well, and it does a good job. The only disadvantage to this product is it will be hard to find, you can probably get a local paint and body shop to order it if they don't have it or Meguiar's sells directly through their web site now.
Both products are spray on, wipe in, then wipe off products. Both contain fabric softeners and brighteners. If you have a really soiled surface to work on you'll want to find a soft bristle brush that won't pull the fibers out and scrub it some after applying the product. This will also even remove stains with pretty good ability. I use the all purpose cleaner and it removed stains from the carpet in my house that I had long ago determined were permanent.
*I don't work for Meguiar's, I'm just a huge fan of their products.