I dont have one,. but according to the Amazon web site they cost between £49.99 and £169.99. See here
Amazon.co.uk User Recommendation
As far as I know they are tablets using a heavily modified version of the Android operating system. Because they are sold by Amazon they are trying to encourage you to download material from the Amazon web site (music, films, books etc).
Any reason why you want an Amazon Fire or are you just looking to buy a tablet?
If you just want a "tablet" you may be better with a "normal" Android tablet rather than one locked in to Amazon (unless you expect to buy lots of digital media from Amazon).
I notice many of the Fire tablets only have 8Gb of memory which is not a lot when you consider the software supplied with it will probably take over half of that. I note you can add a Micro SD card to add more memory.