Just because your iPad 3 is no longer able to upgrade to the latest iOS doesn't mean your iPad 3 is suddenly useless.
Your iPad 3 will work as it always has and the apps you have installed on it will continue to update and receive some level of app updates relevent to your current iOS.
You have had four years of iOS upgrades and updates.
Your iPad 3 will still do everything it does now and you will, get, at least, another full year, perhaps two, if you decide you want to wait longer to get a new or newer iPad model.
Your iPad 3 is NOT, suddenly, becoming obsolete or useless.
So, your options are really keep using your iPad 3 or purchase a new iPad if you feel you need or want to.
Your current iPad 3 will still work and continue to receive app updates until sometime through this Fall 2017, when, with the recent introduction of iOS 11, ALL support for older 32 bit iDevices and any iOS 32 bit apps will come to a final end.
Your iPad 3 will still work and function as it always has, but will no longer receive any more app updates after the Fall of 2017.
The final app updates your iPad 3 will receive will be its last!
Your iPad 3 should STILL be receiving app updates, currently, but look for this to end sometime soon.
While I do own a large screen iPad Pro, my wife and I still use and get along fine with both an iPad 2 and iPad 3 models.
Both these iPads are STILL receiving app updates, just like your iPad 3 is still receiving current app updates!
This is why Apple introduced the new, lower cost 2017 iPad 5 model, in April
Apple is trying to get older iPad 2, 3, 4 and 1st gen Mini iPad users to upgrade to more modern iPad hardware in anticipation of the recent introduction/release of iOS 11, which WILL render all older 32 bit iDevices obsolete.
Good Luck to You!