Microphone advice needed please.

Hi everyone, I am new to filming but I must admit I am loving it!  I have a Sony Alpha 55 and am heading out to Kenya again in September.  It's my third visit there but my first at filming as well as stills. 

Which brings me to my question.  I have been looking online at microphones and am very impressed with the look of the ECM-CG50 shotgun microphone but another £200 on top of the new camara, new lens and the cost of the trip is a lot to find.  Does anyone out there know of a cheaper option or would I just be buying cheap/buying dear in the long run.  In other words is there a cheaper alternative or should I just take less spending money to Kenya?

Any advice would be very welcome.

Thanks Karen