Unlike most rep grind mounts, the Argent Tournament Champion Seal mounts pay for themselves, many times over. I'm currently at about 81 mounts (I think), on my way to the 100 mount achievement, and only have the troll 100 seal mount left.
Let's look at what getting ALL the mounts entails.
Each capitol city faction quartermaster offers 2 mounts, one for 100 seals, the other for 5 seals and 500g. All of them (Horde and Alliance) also sell the Argent Hippogryph flying mount for 150 seals.
11 mounts for 2500 gold, 675 seals
Sunreaver or Silver Covenant - 1 land mount 100 seals, 1 flying mount 150 seals.
2 mounts for 250 seals.
Argent Quartermaster Dame Evniki Kapsalis sells the Argent Warhorse for 100 seals to any class, and the Argent Charger to paladins.
1 mount for 100 seals (100 seals more for a paladin)
Grand total: 2500 gold, 14 mounts (for most classes), and 675 + 250 + 100 = 1025 seals required.
Add the teleport Tabard, and if your toon isn't an engineer, you might want the mailbox/vendor/bank option that the Pony Bridle offers, for an extra 150 seals.
Tabard and bridle = 200 seals.
I've already bought the tabard, and since I already have Jeeves, I'm very doubtful I'll go for the bridle, even though it does give you an achievement. Why not? Urggghhh, I am very, very, verrrrry tired of doing those AT dailies. Yes, it's a nice amount of gold, but it's a time-sucker, when I want to be working on other toons.
Let's break down how long it takes to earn 1025 seals, using only the dailies, once you're exalted with Argent Tournament.
3 seals + 3x(13.23 gold)= 39.69 gold from Sunreavers or Silver Covenant tent NPC's.
7 seals from the Argent Tournament tent. 6 quests, but 7 seals since TFA gives 2 seals. These quests also reward 6x(13.23)= 78.78 gold + 40 gold from the grab bag = 118.78 gold, plus the chance of extra Champion seals dropping occasionally from the bag.
So, 9 Daily quests, 118.78 gold, 10 seals per day. Let's also toss in the Heroic Trial of the Champion for an extra 3 seals, bringing us up to about 13 seals per day, give or take. I usually specifically do heroic TOC first, while doing quests, then do my random for Frost badges after that. Sometimes, you get TOC as the random, so you could have 16 seals that day.
1025/13 = 79 days. Well, really, 1075/13= 83 days, since you're definitely going to want to get the tabard to minimize travel time to the tournament grounds as much as possible. This is assuming you do all the dailies plus TOC every day, 7 days a week. Assuming you do this, 83 days times 118.78 = 9,858.74 gold. That's a profit of almost 7,400 gold, even after you pay for the 500 gold mounts.
So if you ever see a level 80 whining about gold, tell them to go buy all the Argent Tournament mounts. They won't have to worry about gold for a long time after that.