Most heirlooms only work in a limited level range in their default form and must be upgraded to work at higher levels. That costs gold, and you’ll need around 30,000 gold to outfit yourself with a fully upgraded set (counting only those that give you bonus experience). You may need to spend some time on a boosted character to acquire the gold you need to outfit another character with heirlooms, but it’s well worth the effort.
Taerar - Alliance Taerar - Horde Talnivarr - Alliance Talnivarr - Horde Tarren Mill - Alliance Tarren Mill - Horde Teldrassil - Alliance Teldrassil - Horde Temple noir - Alliance Temple noir - Horde Terenas - Alliance Terenas - Horde Terrordar - Alliance Terrordar - Horde The Maelstrom - Alliance The Maelstrom - Horde The Sha'tar - Alliance The Sha'tar - Horde The Venture Co. - Alliance The Venture Co. - Horde Theradras - Alliance Theradras - Horde Thrall - Alliance Thrall - Horde Throk'Feroth - Alliance Throk'Feroth - Horde Thunderhorn - Alliance Thunderhorn - Horde Tichondrius - Alliance Tichondrius - Horde Tirion - Alliance Tirion - Horde Todeswache - Alliance Todeswache - Horde Trollbane - Alliance Trollbane - Horde Turalyon - Alliance Turalyon - Horde Twilight's Hammer - Alli... Twilight's Hammer - Horde Twisting Nether - Alliance Twisting Nether - Horde Tyrande - Alliance Tyrande - Horde Terokkar - Alliance Terokkar - Horde Thermaplugg - Alliance Thermaplugg - Horde
Though related, this is no longer true. You can now purchase a lvl 90 character boost. Some power levelers have hoped for a day when you could use real money to buy individual items in-game, some times called "micro-transactions." At a Game Developers Conference 2008, Rob Pardo gave a strong indication, Blizzard would not ever go this route with World of Warcraft.
Edit 20 It’s been a week since this post and a lot of people are still reaching out to me with questions which is fine. I have had a few different people reach out to me to help make YouTube videos based off this guide and more info in BFA which I’m more than willing to do. Whoever gets the videos up first I will link them here for you guys to enjoy.