It also depends on whether or not you're looking at purchasing the SRT version of the Roadster.
Both cars feature the Mercedes M112 E32 engines, the SRT ups the ante with the AMG version of the E32 (E32AMG). All Crossfires manufactured have the same engines throughout the build years. The SRT was built only in '05 with just a few carrying a '06 manufacture date; 2016 Coupes, 958 (?, help me out here SRT Roadster owners) Roadsters so the SRT's are in a pretty exclusive club. The prices for the SRT's probably won't stay cheap for much longer.
If you're coming from Porsches the cost to maintain the Crossfire, regardless of what version, won't be too shocking: 8.5 qts. of synthetic oil, tires aren't cheap (as mentioned above), premium petrol only not to mention the cost of Mercedes parts (forget that these are Chryslers; darn near everything you're going to end up fixing or replacing is Benz) so it certainly isn't an inexpensive ride.
BUT, it's worth every penny !
You should tell your SRT-owning friend to join this forum: he'd learn a lot!
Since I don't own a Roadster (yet!) I can't comment on specific issues with the car but suffice it to say that I haven't spent a dime on repairs to either of my cars besides the normal TBA stuff. The SRT is pushing 57K, the Coupe is at 62K (I think, it's my wifes & I haven't peeked at the odometer lately). Besides replacing some bulbs & some warranty CD player issues they've been flawless!
I hope you find the "right" car & welcome to the best Crossfire forum around!!!