The ones you found at the merchant are Apprentice 2, not a significant upgrade. There are a few ways you can get spell upgrades:
- Buy them from the broker. You've already found that can be expensive. Check back frequently as availability always changes.
- Get lucky and find them as loot drops. Most of the time, though, the spell will be for another class.
- Craft your own. Based on your adventure class, begin a career ar the corresponding artisan class that can make spell upgrades.
- Ask someone to make them for you. Right click > Chat Options on your chat window and select the Crafting chat channel. Then start asking if there's anyone that can make upgrades for you. They usually charge a minimal fee. They can make up to Apprentive IV with almost no cost. Adept III's, however, require a rare component and will cost much more. If you provide the rare, the cost will be low.
If you don't find any takers in the crafting channel, ask your guild crafters to make them for you, assuming you are in a guild.
If you are still having a hard time, come on over to Najena. I can help you get those upgrades, as I'm known to just throw my money around to anyone that asks me. :)