Remember in the camera world you get what you pay for. Theres really no such thing as a great cheap anything for cameras, audio equipment, ect (unless maybe your buying some old classic manual lenses).
What are you going to use the mic for? Shotgun mics really do not do a whole lot from my experience. Obviously they are better then the built in mic for the most part, but do you really need it?
Do you want better audio for ski edits? Shotgun mics really would not do too much if thats the case.
Are you trying to capture talking for some sort of other video?
I just really do not see great purpose for shotgun mics personally. If you want to record sound for skiing and want it to sound good, I would recommend just recording it separately from video using a boom mic or wireless. I guess you could use a shotgun for that too, but I dont know how much better it would be then your built in.
If your going to drop 250 on a shotgun mic, I would recommend saving a little more and getting some relatively cheap wireless mics. You can do SOOOO much more with them and have a lot more purposes then a shotgun mic.