Very cheap for you enthusiasts maybe. For non-enthusiasts a cheap card is 50 bucks. Midrange 80, High-end 100, 120 if we want to go overkill. Not to mention always the same thing: if it's for mining, it's trashing money. If for learning, better to upgrade the whole system.
you can find it for 50 buck even new lol
750ti is very cheap
Link please. Here's what I can get for for 50 bucks from my favourite etailer: ASUS nVidia GeForce GT 730 903Mhz 1Gib GDDR3. 64 bit bus. That's sure going to be very similar in performance. No trace of those on amazon.co.uk, but I'm sure I suck at it.