No, it's definitely a mistake.
Firstly, it was pointed out on the scanlator's website, and their translator acknowledged he made a mistake.
Secondly, here's the panels in question untranslated:
http://img204.imageshack.us/img204/4275/panel1x.jpg
http://img442.imageshack.us/img442/8150/panel2o.jpg
See that character after the 7 and the 10? That's the character for ten thousand:
http://www.df.lth.se/cgi-bin/j-e/jis...1B%28B&WC=none
So Lucy's rent literally translates as 7 ten thousand, and Fairy Hills rent translates as 10 ten thousand.
7 ten thousand = 70,000
10 ten thousand = 100,000
One, Levi's not a crappy mage, just not one as combat oriented as the main characters. Two, consider who they work with usually. Levi usually works with Droy and Jet. Two guys that had/have a crush on Levi, and have magic that's not particularly large scale. Lucy usually works with Natsu, Happy, Grey, and Erza. Natsu's known for his collateral damage, Erza and Grey aren't too much better, and Happy considers Lucy's need for money to be something to make fun off.
Care to guess which of the two loses more of their pay check paying for damages?