Suzuki are without doubt the cheapest to run, and very reliable..
Just a matter of what model you want...
Had an Aprilia RSV 1000, that was pure pleasure..until the cost of parts...oh my god...never again
Honda, again the parts are expensive...
Yamaha, R6 or R1 cracking bikes...almost on par with Suzuki for reliability and parts
Had many bikes over the years...i am now back on a Hayabusa, which without doubt is the best sportsbike money can buy