"should I fess up and get a flying mount or spread the wealth and get my 60+ alts the 100% riding skill?"

You never quite explain /why/ you can't do raids or gear up for Heroics, so I have to be a little vague. Long story short, being able to fly will enable you to earn money and get things done much faster. I heartily support getting basic flight as soon as possible, and then epic flight as soon as you can afford it. The upfront costs are substantial, but there's nothing compared to the convenience, cost savings, and improved efficiency of having your own flying mount.

Me myself personally, I saved every copper I earned while leveling, so I had more than enough cash on hand for flight at 70, and Cold Weather flight at 77. Then at 80 I worked my DK's tail off for several days, then raided my other characters' pockets to scrounge up 5,200g for epic flight training and a snazzy red gryphon. It left me completely broke for a few days, but that new gryphon allows me to get my dailies done faster, and to clear those one-time quests that I left behind in the rush to 80. I repaid the money I'd borrowed from my alts (roughly 1,500g) in nine calendar days, and I could have done it faster if I'd had more time to play. If you're saying you currently can't fly at all, I support flight training even more strongly; many parts of Icecrown and Storm Peaks are inaccessible by ground, so you're missing out on a significant amount of content.

The most common cash reward for a high-level daily quest is 13g23s. Some are higher, some are lower, but I think that's a reasonable average if we're not concerned with finding *the* optimal route. With a limit of 25 per day, a devoted adventurer can earn 300g per day just from dailies. Beyond that, there's also material farming or cleaning up those one-time quests that I mentioned earlier (the Exp-to-cash conversion isn't what it used to be, but regular ol' questing still pays well).

On a side note, those daily quests will also help you build reputation, which will help with the Heroic and raid gearing. I did my first Heroic dressed in blue quest rewards and gear I earned at Honored/Revered with the various factions. It'll take much longer to build rep with dailies than you would by championing, but you'll get there eventually. Check the Lichborne column to see which factions have the best DK gear.