First question - Do you need Photoshop or is Lightroom sufficient for your needs, I ask that because you can buy a stand alone version of Lightroom 6 from Amazon for £106.
I very much doubt if you will find a genuine copy of CS6 for sale now,you will certainly find pirate copies but who knows what you would get, so its not really a good idea apart from the fact it's illegal.
You might pick up a copy of an older legit version which may be all you need, I seem to recall that Adobe were giving a free download of CS2 at one point but I don't know if they still are
The Abobe CC plan for photographers is £8.71/month and has not gone up since Jun 2014 ( well I am still paying the same and have renewed for 12 months) and this gives you both Lightroom and Photoshop with all the updates and Adobe help if needed for the price of 2 or 3 pints of beer a month ( depending where you live).
Personally I would go for the subscription but download the free 30 day trial before you commit yourself