OM-D -> 550D, inexpensive lenses I should get?

I sold my OM-D E-M5 to get a 550D for a lot of reasons, and I feel my decision was spot on and one of the better decisions I've made this year, with the money I have left-over ($700) I can fund a lens or two, but I'm unsure on what to get.

I grabbed the 550D with the kit lens and grabbed the 50mm f/1.8 II for obvious reasons, with the $700 I plan to grab a lower-end external microphone but I can't decide what lens or two I should go with it.

My main issue is, should I get one fairly expensive lens, or spread it over 3-4 lenses which will extend my focal length, give me another prime for low light, (and I was thinking of getting a shallow fish-eye for handheld video).

Any suggestions are massively appreciated, I'm brand new to Canon and coming from m4/3, a bit perplexed at all these cheap lenses, but I'm already enjoying it.

Cheers.