Honestly IMO your best bet is to go to sonicelectronix like stated before, they are cheap, fast with shipping, and usually include all harnesses and dash kits with any headunit you buy. From there you can either install yourself, or then take somewhere to have installed and save a ton of money. I've ordered from them plenty of times before and swear by that website! Good luck!
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Also, like said before, try not to sacrifice quality for price. In other words, you get what you pay for, anywhere. A $100 off brand HU obviously won't compare to a $500+ Pioneer, but compare specs and features and get what's right for you. Jensen actually makes pretty decent HU on a budget, I went with a Jensen Flip-Out a while ago and it looked/sounded great.
Sorry for the walls of mass txt haha just figured I'd try and help