I have used an iPad since the day they came out (5 years ago now). They are very good, but are at the premium price point. On the other hand, they are extremely solid, and Apple typically provides OS upgrade compatibility for at least 3 years–that is not so typical for Android tablets, and the Microsoft Surface line is too new to know for sure how long they will be useful.
I used my original iPad for 3.5 years before I upgraded to the iPad Air, not because the original wasn’t working, but because it wouldn’t support the latest OS, which I wanted. I got about $100 for it from Gazelle. That tells you how well they hold their value. Gazelle also has a resale store, so you can get used, late-model iPads (and some Android devices) at a substantial discount from new.
iPads have a stated battery life around 10 hours (5 hours if you are constantly streaming video), and that has been my typical experience with them under heavy use. Since I don’t do that too often, I usually go days between charges for mine (and I am visually impaired and turn the screen brightness fairly high, which increases battery drain). Bluetooth keyboards work great, and many third-party companies make keyboard cases that put the iPad into a laptop-like configuration. (Note that many modern laptops also have 10 hour battery life–MacBook Airs and the equivalent Windows laptops using the latest Intel mobile chips and solid-state drives all have much longer battery life than even 3 or 4 years ago. They are just a lot more expensive than tablets.)
I don’t personally use MS Office, but I have heard that the iOS (the operating system of the iPad) versions are very good. Apple has its own office suite which is free, but perhaps not as full featured as MS Office, but will let you work with Office files (though not necessarily with 100% compatibility). Apps exist for all the major e-readers, and you can easily add pdfs and e-pub formatted books from 3rd parties to the iBooks app.
Apple recently announced the newest version of iOS (available in the Fall), which will make the iPad more of a productivity tool. Only the iPad Air 2 will support every new feature, but every iPad produced in the last 3 years or so will get the upgrade and at least some of the new stuff.
My mother had a Kindle Fire that only lasted a couple of years before crapping out. She got a new iPad Air (the 2014 version of the 10" form factor, so 1 year out-of-date) for about $100 below original list price. She loves it, and it only weighs about 1 pound, even at that form factor. For reading in bed, though, she prefers the even smaller and lighter Kindle Paperwhite.
The large size iPads start at about $500, the iPad minis start in the mid-$300 range.