thing... you mention you set yourself a 6 day max,
I don't fly that much! It's a
sixty day self imposed limit...
. It's not the actual flying bit of the approach I get rusty on, it's the procedures. There's a certain lingo and way of doing something like an NDB hold and approach and I don't like to be one who goes 'Err...' on the radio, I like to keep it sharp.
but what is the 'average' dry cost for something like a 172, and how much in fuel does it cost per hour?
It varies wildly. I pay £96 hr for our 172's and Warriors, that's wet and brakes off/brakes on. Further south the price goes up substantially for some reason. Most (in fact all hire rates I've seen) are wet, but if you do find a dry rate then you can reckon on burning around 30 litres/hour with something like an 0320 engine ie your average 172, Warrior type a/c. Fuel is around 1.50 a litre up here so £45 an hour fuel burn. An 0360 will give you on average around 35 litres/hour and an 0540 around 40 litres. This includes start up, taxi, climb etc. The actual cruise burn will be less.
This of course assumes you know how to operate the engine correctly. One of our club members took our 182 to Germany and he was getting around 60 litres an hour burn because he never bothers twiddling the red knob. It's like burning £20 notes. I fly an Arrow on occasion which usefully has a fuel flow gauge. The difference between running it fully rich at 3,000' and leaning out properly is around 18 litres an hour, or £27 worth of fuel...