I was planning to farm Zul'Gurub for the mounts yesterday until I stumbled upon a lvl 64/65 Hunter that wanted to join. He was willing to pay, so thinking back at this topic I asked 100g per boss. Eventually we got the price down to 60g/boss and we did all 8! He was going to loot everything he wanted and I would get any mounts if they'd drop.
This meant 480g for 8 bosses and about 120g for the money drops (about 3g per character per boss), so 600g total! It took me about 90 minutes to do a run, but I feel I can do it in 60 minutes next time.