I am after a very cheap and light device that I can use for basic web functionality worldwide (well as wide as possible), i need it to use mobile data rather than wifi as finding wifi can be very frustrating.

A friend of mine used a kindle for email and very basic browsing during a round the world trip a couple of years ago but I understand that the kindle can no longer be used like this.

Are there any other options ?

A used iPhone or Android. Or a cheap new Android phone.

A Windows Phone. Those things are dirt cheap (the lower end models), and can be had unlocked for peanuts.

Yes sorry I should have been clearer, its the Amazon Whispernet 3G type service I am struggling with, basically a 3G (or 4G) mobile data network that I can access globally at a reasonable cost. Normal mobile data plans are so expensive and restrictive that I don't want to go that route if there is another option.

Plus long battery life would be a definite plus and most iphones/androids struggle to get more that a day.

http://www.microsoftstore.com/store/...devices_WinPho

Lot of these are sub $100, and unlocked. Battery life is pretty awesome. The Windows Phone OS is simple, easy to use, and is not a battery hog.

Check out the T-Mobile worldwide data plans, maybe with a tablet.

http://www.t-mobile.com/optional-services/roaming.html

I haven't used them, so can't tell you firsthand how reliable they are.

Amazon has shut people down from using Kindles for this type of thing. If you want to use cellular networks, your only real choice is to use an unlocked smartphone. Cheapest option is to buy a local prepaid SIM for the country you're in.

The earlier kindle 3G cellular+wifi model was incredibly slow with wifi, 3G was worse!

Lots of options if you want something phone-sized.

If you want something a little larger, but without a keyboard I was looking at a ~$200 unlocked Huawei 8" tablet with a reasonably decent processor, screen, memory, and set of bands ("Huawei T1-821L MediaPad T1 Pro (8 inch) 4G LTE Unlocked") but it seems to no longer be available new from reputable sellers. I'm sure there are other similar things, and if you want something cheaper there are slightly
If you want a keyboard, and something slightly larger, there are Chromebooks with mobile data support which are far and away the cheapest laptops with it. Not sure how easy they are to unlock, but there are locked-but-off-contract Verizon ones at Best Buy for $199.

As noted, it is mostly the cheap and light portion of data which is more of a challenge.

If you only need a few MB per country just a few times each year, a pan-international roaming sim might be ok. There's also prepaid sims which roam regionally if you plan on traveling mostly to Europe vs parts of Asia.

For more data with wider options but slow on an annual cost, TMobile Simple Choice data only plan or Google Fi run about $20-30 per month.

A dual sim phone like Moto G dual (smaller screen = weight savings) or Asus Zenphone is a decent option if you want to put a roaming sim in one slot with the option of a local sim in the other. You can search for devices by weight and network frequency support here:
http://www.gsmarena.com/search.php3
Add an inexpensive battery pack or search for high capacity/replaceable battery.

One thing I'd advise when looking for an inexpensive travel smartphone - check the build quality of the sim slots, either via YouTube reviews/unboxings or in person. Some of the really cheap phones (cough cough Lumia 520) have scratchy sim pins. If you are swapping sims in and out, plus want to keep them in nice condition, get something with decent build quality. You don't want a pin to break off or sim to get stuck, as finding the right data solution can be the tricky part.

So based on this post I looked at this and after reading the reviews I bought one of these (Neutab G7)- and now I wish I'd bought two of them- it's since been pulled from Amazon's site.

This is a pretty great deal @$70- it's Dual-SIM, unlocked, runs Android 5.1.1 out of the box, pretty speedy with no lag (which is rare for cheap tablets) and just runs well. I'd planned on using it with a "leftover" 1G/mo SIM I have laying around to be a Bluetooth Media Player in my beater car, and I could use for Nav as well, but I've been using it as a WiFi HotSpot in hotels (finally using that T-Mobile Data Stash before it runs out at the end of the year).

Hopefully it'll come back to Amazon. It was even 2-Day with Prime.