I get 27 mpg towing a 1250kg trailer with a boot full of jerry cans and clobber. When I read of people saying they get ~20mpg I assume they've been driving like they're doing a bank job, or shunting around town a mile here, a mile there, on a stone cold engine.
I'm not suggesting a petrol turbo is a miser's choice for one minute, but equally anyone thinking a modern diesel is a cheap ownership proposition has yet to experience injector / pump failure on a diesel.
If fuel cost is a bother, the best way to deal with it is to review how and why you use your car. If work is <15 miles away, cycle - I hate driving to work, it's a waste of my life averaging <30mph and a very boring way to dispose of petrol.