I run a Small builder Co that specializes in decks patios and carports. We pull a lot of sails down. Cheap sails are a temporary fix. A quality sail professionally installed that will cover 2 cars will cost at least a few thousand.
Cons
A lot of builders are reluctant to attach sails to the house as it requires penetrating the house roof and flashing the rear posts through the roof, a recipe for leaks. If you are going to do this, get it done professionally, and ensure the posts are attached down to the Top plate, tie down is crucial in big storms.
The alternative is to have 4 freestanding 120 x 120mm posts into massive footing 600 x 600 x 1200mm deep. $$$$ and ugly as they are usually smack in front of the house.
Sails are not insurable, they are, as knuckles I think mentioned, fucking dangerous if a shackle lets go. They'll kill ya!
They go moldy and look older than they are and are prick to clean.
Pros,
In terms of materials sails are probably cheaper than a steel carport, (but a steel carport would be easier to install yourself, so you would save on labor).
Sails do not need council approval.
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My opinion with few assumptions.
I would suggest buying a kit from someone like "Stratco", look at the sanctuary product maybe. Assuming you are putting in front of the house you want a product you can attach to the house.
NB suppliers like Titan and other shed co's do not have engineering to attach to the house so you end up with ugly posts in front of the eave or up the wall.
Stratco has engineering to attach to the house and supply rafter brackets enabling you to attach the back end of the roof to the house trusses. If its a high house, it straight on the wall.
If you want to go down this track and want some help with the kit spec side of things, let me know exactly what you want to do (attachment wise, budget etc) and I can point you in the right direction. But if you are looking for a real cheap solution, it gets hard, you know the one, "Ya get what ya pay for"