Brand's mana costs are overall lower than Morgana's, including Black Shield.
50 vs 50 (Sear vs Black Shield. Dunno why this spell is 50 mana but whatever)
130 vs 110 Soil vs E
120 vs 110 Binding vs Pillar
At early levels, they start off about the same but Morgana's spells scale upwards further than Brands. Morgana feels like she's annoying mana wise because all you see her do is use Soil to farm the wave safely where as other casters would have to use more mana/more than 1 spell that early on to clear a wave. That and she's a prime candidate for Catalyst, making her seem even more efficient.
Compared to most other casters as well, Brand's spells tend to be a bit lower. Sear costs less than Body Slam for example. Or even taking Sear/other casters low mana spell out of the equation, he's a bit on the low side besides his ult, which is about on par with most other casters.
Either way, the point was that his Mana costs aren't high like a Heimer/Anivia caster that you're constantly hogging blue buff and eying Catalyst from the get go and that you could run other yellow runes besides mana.
Edit: She got nice boobies.