i've had mine a year now and given me no major problems at all, only a new oxygen sensor in the exhaust due to it being sat in a showroom for 6+ months and iv'e heard of a few others with the sensor fault due to a period of time not being used. got new sensor for £70 so i cant complain at all, on the rareness side of things my 300's finally met another 300 which belongs a matey living in the same block of flats as my mate does. mines red the other ones white and they look good together lol.
my running costs since i had the 300 are...
2 new rear tyres £125 each
o2 sensor £70
30000mile service £225 @ lexus reading
mot £45
insurance about £1000 just above last year, just below for this years with all mods declared.
cleaning products, lots of meguiars probably £100-£200 a year.
other mods like dash leds replacement horn and things about £100
Petrol £40-£50 per week to 10 days do about 15 miles a day in stop start town traffic.
Done a quick add up and with those figures with 2 years insurance 52 weeks of petrol and the rest worked out at a yearly running cost of...
£4970.
I cant think of anything else that i've had to pay out on the car in the last year so that should give you a rough run down on what to sort of expect mate
I was lucky with mine as most of the modification had been done by previous owners so i didn't have to fork out £7500 (got reciepts) on Hks suspension and exhaust, ice installs etc, and other things, so you can also see how much you could end up spending if the mod bug hits you it can tally up to thousands like with any car.
but i absolutely love mine, i know its quick but just dont try racing against anything with more than 300bhp, oh how i would love a charger lol.
nearly forgot the goode olde roady tax which is £215 a year so bump that final price up a couple of hundred.