Would really disagree on that. Owned a Suzuki SV650-S and now a GSX-R600 and both are more expensive than a car.
It may get 40mpg to my car's 30, but it's using higher octane. Also you burn through tires much faster and simple things like an oil change are outrageous if you don't do it yourself.
And then there's the speeding tickets
Yeah, you can get a low end bike and have it be cheap, but then you can also buy a cheap Honda, abuse the crap out of it and get 100-150k miles out of it easy.
I'm look at living in a boat costing more than a house too. But I'm still mentally justifying certain costs like, yeah, a new set of sails may be $$$, but how much does a new roof on a house cost? Home water heaters, air conditioners, plumbing going bad, having to re-sod your yard because the housing association thinks it's the wrong type of grass, total home repaint, driveway re-pavement, termites, etc, etc, etc.
And it still won't take you to the Bahamas
I currently own a SV 650 that I bought for $3000.
A new GSXR-600 costs around $8000. (correction $10,000) I just checked.
Standard 600cc bikes are more like 8K
New cars cost about twice as much.
I will admit tires and chains cost to keep up and, a fool on a bike can toast a tire and chain in 3000 miles.
Oh and only the most high performance motorcycles need premium to run. My 1200cc Suzuki Bandit runs fine on regular octane gas.
The speeding tickets are not a function of the motorcycle or the driver.
However, my over three decades of riding (not pulling credentials here -- just letting you know where my opinion comes from), strongly suggest that motorcycles are a very economical alternative to owning a car.
Please see my post above on the Ninja 250, a very capable motorcycle.
I'm not going to get into a debate about edge cases. Anyone can come up with specific examples to argue against a generality. My own example of the Ninja was just that, I will admit.
However, very few new motorcycles approach the purchase cost of a new car. While they usually have higher maintenance costs, over the long run they can still come in cheaper.
In the end, they are simply a different form of transportation and anyone making any sweeping generalized statements about either is comparing apples and oranges and is often trying to make the data fit their opinion.
As for costing of a home vs a boat, we are going through the same thing right now. For us, the boats we are looking at (45' range), with slip, insurance, utilities and $6,000 a year in maintenance plan are less than the load of supporting the 1100 sq/ft condo in the middle of Seattle, so it makes financial sense for us.
Back to the point though...the argument that motorcycles can't be cheaper to purchase, own and maintain than a car is not a valid one. Not in my experience as a motorcyclist, MSF instructor and having worked at motorcycle dealerships over the years.