Welcome to the world of X-Plane.
Do your conversion rates between US dollars and British Pound. I think you will find the UK supplier mentioned below will still be more expensive as they will have their mark up and other internal costs as well.
Don't waste your money on a "Steam" version. This is a 3rd party company that has no connection with the developers, Laminar Research (LR). LR have done all of the development work and this 3rd party company is taking a financial advantage of that development with no input. Laminar Research offers no support for the Steam version.
At this stage XP11 is only available as a digital download LR. For me personally I am waiting for the boxed version. Should you decide to go for the full digital download it will take time so be patient.
The genuine LR version, when installed, and provided you tick the relevant boxes, will be automatically updated every time you start XP. This is the situation with a disc version as well. From other readings in this forum Steam version updates/upgrades will have some delays.
I understand the current version is a "global" edition with some restrictions on where you live ie if live above the 40 degree parallel latitude, north of the equator, then you may not be covered for scenery ie if you want to fly locally otherwise you will need to select other airports further south in the UK.
There are other postings in this forum where this has become an issue for those living in the vicinity of Norway, but I understand LR are working on that problem. Raise the question of your locality directly with LR at the following link email@example.com Randy should be able to help. By the way, ask when the boxed disc set will be available.
If you go for the digital download make sure you have a full backup kept in a safe place. When XP installs it will be in its own directory. The program does not load into other areas/directories like some programs do within say Windows. It is a standalone file structure.
Here is a link for the UK that I know sells X-plane but they are taking orders at present. They may also want to sell you a "Steam" version. The link is at http://rcsimulations.co.uk/ The company is in Bristol, Bob and Carol should be able to assist. Their contact details are available on the home page I have referenced above.
Are you aware that XP11 is a 64 bit system whereas the software you already have is only 32 bit. As you say you intend to test the download first. Good move as it will also advise you on whether it will work or not on your existing PC. If it is old then most likely it will be 32 bit.
I could go into a lot of other info about a computer system. Have a look at
http://www.x-plane.com/2016/11/x-plane-11-system-requirements-announced/ , Go for the recommended rather than the minimum requirements
If you are in the market or need to purchase a new PC have a look at https://www.youtube.com/watch?v=j_YQMSeNM-M Michael is the recommended PC supplier by LR in the USA. In this instance initially disregard his comments about yokes and pedals but take on board his comments about what type of pc to purchase. The yokes and pedals can come at a later date as you become addicted to flight simulation.. MIchael has a lot of other useful information which helps you to further develop your system. Have a look at the following link at https://www.youtube.com/user/col2mab/videos?sort=dd&view=0&shelf_id=0
My thoughts on the Joystick. I have the same unit but replaced it with another unit. I am of the opinion that it is one of the low end units available. However, there are other flight simmers who use this forum who have the same unit and fly successfully. My suggestion is to use the Logitech unit and if you get "hooked" on flight simming then progress to a more advanced or better quality units as described by MIchael above.. With the unit you have you will need to program the "keys and buttons" to get it to work effectively.
Hope this helps and good flying.