new tyre advice needed

I'm looking for a replacement rear tyre (140/80 R17) for my Guzzi sidecar outfit. I normaly chose tyres by finding the most recommended tyre on a single marque forum and go for that, but I'm not having much luck on this one.

I don't want to change the wheel as it's expensive and complicates the insurance, but as it's an outfit bike tyres get squared off and hence worn out quite quickly.

I can find lots of advice on good performance but not much on which tyres last the longest for the least money. Obviously grip isn't important compared to a solo, in fact slippy tyres are actually an advantage.

I notice adventure tyres are available in that size, be useful in the snow and a deeper tread would give longer life?

Any advice on a cheap, rock hard slippy tyre would be much apreciated!