You might not be able to afford buying Thunder, but you are most certainly able to sustain it once you do have it.
In fact, one of my friends recently started playing on Alexina and we helped her get Thunder since she didn't have the money to buy it, having just joined the server and all... It was the only skill she ranked (r2 now with double rainbow help) along with Magic Mastery and the music skills, now she can raft for Mana Herbs as well as other profitable items such as Iron Ingots and Tipping Suits thanks to it, she was even able to buy her own Glowing Gargoyle statue and take care of all her other needs with just the Thunder skill.