I want to buy an avic-8000nex, but I'm not sure where you buy it. I'm gonna buy it online as none of the 5 shops I visited in my area sell it.

I see the unit on ebay going for under $1k and then there are the authorized online retailers that have it for $1399. With all the adapters and harnesses needed its ~$500 cheaper to go the ebay route.

Assuming something went wrong and the unit needed to be repaired, what would be a ballpark price to have the unit serviced/refurbished/repaired? $150-300?

Are most of you guys who are installing your own buying online? 

I purchased mine from Ebay store, and it may be a crapshoot. Pioneer says they won't honor warantee from an unauthorized dealer. That is BS in my opinion, but who am I to say. I have purchased over 250 items from Ebay or online stores, and in the few times, the item was defective, they were replaced or refunded. So really, it is your call. It is a no-brainer for me.

Mine came off of Craigslist at a STEEP discount. It was only slightly used (for about a week) and I didn't have any problems with it. I have seen units going for as little a $500-600 (yeah, 8000NEX units) you just have to be diligent in your search as they go fast.

Also - as far as repairs - good luck. Pioneer isn't even selling some of the most basic parts for the unit yet = it's impossible to get a power cable right now. So be careful, make sure everything is included.