sonicelectronix.com is pretty good for prices on harnesses and dash kits. I thought 2003 was still considered a Gen II and had the same dash panel assemblies. You can always call them and ask, and they would be able to tell you exactly what you would need.
I started an Official F90BT Installation thread, which has links and pics in it of where I got stuff at, what I did in installing it, and the associated pics.
As far as the F90BT itself goes, you should have decent results googling it and then following some of the results that come up. I bought mine as a factory reconditioned unit from CarToys.com for around 500.00 I haven't checked Ebay for them, but I would say that if you do go the remanufactured route, make sure it's from an authorized Internet reseller. Pioneer has a list on their site on who they acknowledge as such.
As time goes by, the F90's will go lower as some of the perpetual upgraders move onto newer systems. If you don't mind the used gamble, then something should turn up on Ebay.
Another option is to take a look at NYC's Avic D3 that he's got for sale in the Auto Parts For Sale thread. He's offering a lot for what he's asking. The D3 is one model older than the F-series, but it's extremely close in functionality and a rock-solid performer.
Good luck. We're here to help as much as we can. I was in your shoes too.
TRU
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