... they usually last a couple of years before they start to loose their shape and or fray. This particular hat is about one year old now and has the lost the slight curl to the sides of the brim and the indentations at the top front center of the crown are almost gone.
When the weather cools off it is easy to re-form a straw hat. Softened the straw with a wet cloth or water spray, stuff the crown with newspaper and stretch rubber bands around the outside to contract the headband. Form the rim like you like it using cardboard or rolled newspaper as a rough form. Hold everything in place with rubber bands and string (or anything else handy) and place the 'boxed' hat in a warm dry place to dry. Attics are handy.
Frayed edges can be stitched or overcast. Yes, that is a lot of work to preserve a $1.69 ($4 to $7 around here) but it doesn't take long and by the time it needs to be done it isn't a cheap hat any more, it is an old friend.
Do I do that with my straw hats? Depends. If I like the hat and we have some history together I work harder on maintenance. On the other hand hats that never seemed to suit me and ones I associate with frustrating projects or trips I don't.
Hint: straw hats will eventually adapt to your head shape but tend to get too lose with time as they continue to expand. You can speed the adaptation by moistening the straw and wearing it until dry on a cool, sweat-free day. Or wear it while sweating and then dry it in an attic or freezer. Once the hat is formed to your head you can keep it that way longer by rigging a band outside the hat to stop the straw from expanding any more. Cloth, a bit of leather, ribbon or woven cordage all work - be creative.