i race my yz250f and my oil costs 10bucks a quart changed every week or so. top end has to be changed every season that costs about the same as a top end rebuild for a banshee. the only thing is I can change a banshee top end myself. the 250f is a whole diffrent story.
I agree that 4strokes are cheaper but there are 2 type of four strokes. your honda trx3004x4 is going to be 100times cheaper then any 2 stroke. but then again your yfz450 is probably going to be in the same range if not more.