I made around 40,000 gold with a 5,000 gold investment, and some DKP spent.
I play on a server where we farm BT in my guild, and I recently bought a ton of Heart of Darkness, had almost every BT / SSC BoE pattern, BoE crafted items, anything available to a BT farming guild, and transfered my 70 alt to a non-progressed server. For 25$ and 5000 gold, I have made over 40000g. Heart of Darkness cost me 250g, and sell for 1,200 ea. on the new server. Do some research before you transfer of course. Heres a list of stuff to look at in the AH:
Primals (Air, water, earth, life, etc.)
Enchanting materials, mainly Large Prismatic Shards (Also - level 60 stuff like illusion dust / large brilliant shards - BULK ONLY)
Epic patterns (Duh)
Heart of Darkness (Duh)
Fel Lotus (Bulk)
Flasks (Bulk)
Cheap epic items (Risky)
Big investment, big payoff. Good luck! It's like buy low, sell high, but cross-realm version.