Interested in you saying Roadsters being cheaper, not something I've ever found. One thing I would say, if you want to go track day racing a lot of places will say that you'll need a roll bar if you have a Roadster so you'll need to think about this.
I think general maintenance is reasonable BUT you will get hooked probably on modification and this may get expensive.
Other main point is that we do go through a fair amount of petrol but it's worth it to hear that noise.
Unless you're into your working on your cars I'd recommend spending some more money and getting a really well maintained (most are) one, it'll save you in the long run. I think I paid top dollar for mine but it had been serviced every 3,000 miles for the last 4 years and treated to £4k of upgrades too, including that expensive clutch replacement.
Roadster for me though. Top down, heater on