I seriously think it's impossible to compare prices market to market. I've been looking at a used CPO i3 for almost 3 months with very very specific mileage, options, color, etc. I was willing to ship cross country if necessary but the prices I found in certain hotter markets (namely those with a lot of DC chargers!) were more expensive than I found more locally.
I lucked out and found a car 99% perfect to my specs (I have a spreadsheet with over 140 used i3s with pricing, miles, features, location, etc over 3 months) for just under $25k for a 2015 with under 15,000 miles, CPOE, and the only feature I didn't get was the interior package (wanted Giga, accepted Mega).
Overall, for what I got and comparing it to the 140+ other similar vehicles around the country, I ended up saving almost $3000 -- plus the dealership is only 13 miles from me and free car washes and charges for life is nice to have only 13 miles away.
If you are patient, you WILL find a better deal, and if you're willing to ship it you may be in an even better position for savings.