Camera has a black spot that won't go away?

My camera has a strange black spot in the top right corner of every picture that won't go away. I have tried cleaning the lens and the sensor but it is still there. The black spot is small and rather blurry but very visible in every photo. My camera is an SLRD Canon XSi Rebel. It appeared when my grandmother used the camera to take pictures on a snowy day and it was snowing. The lens was not replaced or anything during that time. Any idea what it may be and how to fix it without spending tons of money on repairs? Thanks!