Generally from what I've seen most balanced cable upgrades for the HD650 start at around 175$ and go up to the range of 350$.
On a strict budget, I came across this : http://www.shenzhenaudio.com/z-zy-hifi-cable-upgrade-version-hd650-hd600-hd580-hd565-hd525-balance-line-4-pin-xlr-male-occ-zy-002-2-5m.html
They're also listed on Amazon from the same seller : http://www.amazon.com/Upgrade-Version-balance-ZY-002-2-5M/dp/B00A2QJLY8/ref=sr_1_1?ie=UTF8&qid=1399695912&sr=8-1&keywords=sennheiser+HD650+xlr+cables
Does anyone have any first-hand idea of these cables? Pricing looks mouth watering!