Strange thread. I got a 2010 Prius IV without NAV and without a solar panel. No problems finding availability in the Chicago area. I previously owned a 2005 Prius and wanted a 2010 WITH leather (which I missed from my previous cars). But I had no use for the NAV (at $1800 when I already own a Garmin) nor did I want the seemingly useless solar panel. I'm not sure why some posters have the impression that the Prius IV only comes with NAV and the solar panel. Mine sure didn't.
Officially, it's available without either, but some regions have only ordered cars with the navigation system. It's optional in the military sense (i.e., not). Go to Toyota.com, select Build Your Toyota and enter a Philly zip code (e.g. 19153). Select Prius IV trim, then click Next to go to Options. You'll see you can only select two varieties of Navigation Package and two varieties of Solar Roof Navigation package from $2,000 to $4,280 additional cost. No base model is selectable. In Chicago (I tried 60601) you can select a Base Model, but the Solar Roof package without Safety Connect, available in Philly, isn't available in Chicago. Note this is all under Toyota Motor Sales, not under one of the independent distributors (South East Toyota, Gulf States Toyota).
I thought I'd add my $.02 after debating the same thing. I decided on the III - not because I don't think the features are worth the difference in price, but because pushing the MSRP over $25k starts to feel like a much bigger purchase for things I won't use on an every day basis. If you will use them enough to justify them, I think it is worth it - I just won't, and the III already comes with a lot of bells and whistles. Also, for whatever it's worth, I also like the idea of a green car that doesn't use animal products.
.......and I'll add my two cents too. We got the IV and we are happy we did. The leather seats are extremely comfortable, and they remain that way even on long drives. The adjustable lumber support in the driver's seat makes all the difference for me on long drives. I used to stick a pillow behind my lower back with our old Subaru Forester. The three door key-less entry system is very convenient to have. We had a very cool morning recently and the heated seats really made the drive very comfortable. These may not be needed often, but it is a nice feature to have when you can use it. I didn't feel the navigation system was worth the money especially when there are many stand alone units that work much better for a lot less money.
My insurance just said they're giving me $25K for my dead baby. Looks like I'll be getting a black pkg IV!