Step 1: Ignore AH for any Buying reason.
Step 2: Loot everything. Sell Greys/whites/non-"High demand suffix" greens(or DE if you have an Enchanter, and shame on you if you don't)
Step 3: Don't buy at the AH.
Step 4: Avoid spending in the vicinity of an auction related "house".
*cough* ;)

My first 70 was my Hunter. I had slightly over 1k at 70, enough to get flying training + mount right off the bat.
My 2nd 70 was my Druid. Flight Form was nearly free at 68; I had about 1200-1400g at 70.(Which went towards epic flight form eventually)
My third 70 was my Rogue. Lvl'd with my ex's warlock from 60 to 70. He transferred WITH 900g from pre-bc(My ONLY char to EVER EVER EVER go above 300g and that was AFTER an epic land mount pre-bc lol) so he was fine at 70 for getting flying training.
My 2 Boomkin clones are 66 currently. They EACH have 1600ish gold. I blame 2 things for this: Knowledge of Outlands from 3 previous run-throughs, and not needing to buy nice gear off the AH like I did for the other 3. Flight Form will be near-free for them too so Epic Flight shouldn't be far off ;p
My 38 Shaman currently has 200+ gold. He still has lv38+40 training + mount to get though so he'll probably be back down to 100 or less by then. The other 2 shamen are around 100g too, One is a Miner/JC, Too is an Ench, Three has no prof yet, may go skinning to feed Eteo's LW.

Bottom line is, greys = win, AH = consider it a SElling Only house ;p, Live on quest gear; it's sufficient till 70. I can't really give many more tips than that; besides "Don't enter outland till 60 so you don't waste boosted exp gain from Silithus/Winterspring nor waste Gold-earning quests at-70 in Nether/SMV" ;p