Hate to break it to you but that price rise in 470's (even used ones) probably has very little (if anything) to do with brexit.  In fact, prices of both 470 & 480 have gone through the roof due to 1) phase out preparing for release of 500 series and 2) huge spike in demand for good mining GPUs since the huge spike in alt coin prices about 6 weeks ago.  These 2 factors, combined with the fact that the early reviews on the 500 series GPUs are far from glowing (about same hash-rate with more power draw and big issues getting more than 4 GPUs to work per rig), mean that demand for 470/480 is probably near an all-time high, but of course, there is now very limited supply (esp new ones), so as a result, prices of sky-rocketed.  Indeed, I tracked a few sales of used 470s on ebay recently and they went for about $20-$30 more than I paid for new ones about 4-5 weeks ago, just before this huge shortage began.  The new ones are even tougher to get... many ebay and other 3rd party sellers are at least asking close to $300 already, and it seems likely that will go up given the issues with the 500 series. Even though I got a hold of enough 470s to fully stock my four 6-GPU rigs, I[m beginning to wish I would have scooped up a couple dozen for around the $160-$170 each they were only a couple months ago. Live and learn I guess...